ALBERT

Notizen: Anterior pituitary glands of male rats (2, 3, 5, 8, 12, 25, 36, 52, 56, and 62 days of age) were processed for electron microscopy. During early postnatal stages secretory cells are found in various stages of differentiation and comparatively few secretory granules are seen. Nuclei are mostly irregular, and the nucleo-cytoplasmic ratio is large. Many free ribosomes are present; the endoplasmic reticulum is generally sparse and the Golgi complex small or invisible. Cells are of variable shape, and numerous cytoplasmic processes project into large intercellular spaces. Many electron-dense cells which often contain myelinlike figures are seen. Lysosomes and lysosomal precursors are frequently found in secretory cells, predominantly in somatotrophs, of all immature glands. Mitotic figures are numerous in early stages after brith and decrease in number as the gland grows in size. A gradual increase in cytoplasmic volume with concomitant differentiation of cytoplasmic components as well as accumulation of secretory granules, accompanied by loss of myelin-like figures and decrease in the number of electron-dense cells, is observed as the animal reaches the prepuberal stage. Few lysosomes are seen in cells of mature glands. At 36 days of age all secretory cells seem to have differentiated, and morphological features as well as granule content show little change until puberty is reached. Gonadotrophs attain their characteristic morphology later than other cells. Cilia are observed in all developmental stages but are relatively infrequent in the mature gland. The described ultrastructural characteristics reflect the degree of maturation as well as the functional capacities of secretory cells at particular stages of development.

Notizen: Embryos of the viviparous teleost, “Characodon” eiseni, have unusual anal processes that function only during gestation and are lost shortly after birth. This study was undertaken to determine if the fine structure of the process epithelium supports the assumption that these cells have an absorptive function. The process epithelium is a single layer of columnar cells. At peak activity intercellular spaces become very large and isolate individual cells which simultaneously lose much of their cell mass. The cells are characterized by microvilli on their free surface, much pinocytic activity and by the formation of at least four different kinds of vesicles. There is much evidence that these vesicles fuse together. A distinctive characteristic of these cells is a system of tubules and flattened cisternae that somewhat resemble the endoplasmic reticulum yet they differ from it in several respects. It is suggested these profiles aid in fragmenting the cell at periods of peak absorptive activity, thereby increasing the cell surface. Possible mechanisms of food absorption are considered. The fine structure of these cells supports the contention that these embryonic processes serve as absorptive organs during gestation.

Notizen: Under the electron microscope, the spermatozoon of Branchiostoma lanceolatum shows a spherical nucleus deeply grooved along its caudal third, a bistratified acrosome enriched by plentiful subacrosomal material, two centrioles, mitochondria fused into a single mass surrounding the centriolar region which is highly asymmetrical, a 9 + 2 flagellum tilted with respect to the longitudinal symmetry axis of the nucleus. The sperm of Branchiostoma shares the overall features of that of the Tunicata and fits in perfectly with the phylogenetic position of the Leptocardia.

Notizen: The early development of five species of substrate-brooding cichlid (Aequidens pulcher; Cichlasoma bimaculatum; C. biocellatum; C. nigrofasciatum and Hemichromis bimaculatus) is described. Heterochrony in these species renders the standard system of staging inadequate for comparative study. A new system is proposed in which the period of development is resolved into five overlapping phases, each phase corresponding to a dissociable ontogenetic process. This form of staging permits comparison in a way which neither obscures the basic uniformity of cichlid development nor masks the differences between the species.Two special features are discussed: the universal presence in substrate-brooding cichlids of three pairs of embryonic adhesive organs; and the apparent presence of non-neural crest pigment on the embryos and alevins.

Notizen: Oocyte differentiation in the polyclad turbellarian Prostheceraeus floridanus has been examined to determine the nature of oogenesis in a primitive spiralian. The process has been divided into five stages. (1) The early oocyte: This stage is characterized by a large germinal vesicle surrounded by dense granular material associated with the nuclear pores and with mitochondria. (2) The vesicle stage: The endoplasmic reticulum is organized into sheets which often contain dense particles. Vesicles are found in clusters in the cytoplasm, some of which are revealed to be lysosomes by treatment with the Gomori acid phosphatase medium. (3) Cortical granule formation: Cortical granules are formed by the fusion of filled Golgi vasuoles which have been released from the Golgi saccules. The association between the endoplasmic reticulum and Golgi suggests that protein is synthesized in the ER and transferred to the Golgi where polysaccharides are added to form nascent cortical granules. (4) Yolk synthesis: After a large number of cortical granules are synthesized, yolk bodies appear. They originate as small membrane-bound vesicles containing flocculent material which subsequently increase in size and become more compact. Connections between the forming yolk bodies and the endoplasmic reticulum indicate that yolk synthesis occurs in the ER. (5) Mature egg: In the final stage, the cortical granules move to the periphery and yolk platelets and glycogen fill the egg. At no time is there any evidence of uptake of macromolecules at the oocyte surface. Except for occasional desmosomes between early oocytes, no membrane specialization or cell associations are seen throughout oogenesis. Each oocyte develops as an independent entity, a conclusion supported by the lack of an organized ovary.

Notizen: The water mites of standing waters have evolved a novel respiratory system consisting of numerous independent tracheae of tracheolar dimensions. Each trachea has a portion of its length lying directly under the cuticle and one or both ends of the trachea turn into the body to supply some organ. There is no fusion of tracheae to form trunks. Areas of dense tracheation dorsal to the legs supply the leg muscles, and sometimes there is a distinct area of the venter that supplies the muscles of the mouthparts.

Notizen: Two glandular components are described in the genital tract of Xantusia: tubal glands in the Fallopian tube and goblet cells in the uterine villi. Sperm or seminal receptacles occur between adjacent villi in the uterus.Forty ovariectomized lizards carrying a silk loop in the wall of the left uterus were treated for two weeks with either progesterone, estradiol-17 β, progesterone plus estradiol or vehicle. Uteri with loops serving as a local irritant, did not differ significantly from the contra-lateral uteri in any group, hence a response similar to the deciduomal reaction of mammals is not found in this lizard.The weight of the genital tract is similar in sham-operated and in ovariectomized lizards injected with either progesterone or the vehicle. Maximal increase in weight of the tract is noted with estradiol treatment, while simultaneous administration of both steroids is followed by a moderate increase of oviducal weight. Tubal glands and sperm receptacles in ovariectomized lizards injected with either the vehicle or progesterone are smaller than those of the sham-operated or ovariectomized lizards treated with estradiol or with estradiol plus progesterone. Goblet cells are small and lack secretory granules in ovariectomized lizards injected with either the vehicle, or with estrogen or progesterone alone. Both steroids, given together, restore the size and apparent secretory activity of the goblet cells. It is concluded that in this viviparous species, both estrogen(s) and progestin(s) are essential for the maturation of the genital tract in the preovulatory stage.

Notizen: The gross and microscopic anatomy of male and female cloacae of caecilians (Amphibia: Apoda or Gymnophiona) is described and analyzed in terms of structure and function. The arrangement of musculature and cloacal accessory structures is species-specific in males. Contraction of certain cloacal and body wall musculature facilitates eversion of the male cloaca for use as an intromittent organ. The cloacae of females show less marked morphological differences from species to species, and are modified as receptors of male phallodea.

Notizen: The neurosecretory system and retrocerebral endocrine glands of Nezara viridula Linn. have been described on the basis of in situ preparations and histological sections employing the paraldehyde fuchsin (PF) and performic acid-victoria blue (PAVB) techniques.In the brain of N. viridula, there are two medial groups-each consisting of five neurosecretory cells which belong to A-type. The lateral neurosecretory cells are absent. The axons of the two groups of medial neurosecretory cells (MNC) compose the two bundles of neurosecretory pathways (NSP) that decussate in the anterodorsal part of the protocerebrum. The two pathways, after the cross-over, run deep into the protocerebrum and deutocerebrum and emerge as NCC-I from the tritocerebrum. The nervi corporis cardiaci-I (NCC-I) of each side which are heavily loaded with NSM terminate in the aorta wall. Thus, the neurosecretory material (NSM), elaborated in the medial neurosecretory cells of the brain, is stored in the aortic wall and nervi corporis cardiaci-I (NCC-I). The NCC-II are very short nerves that originate from the tritocerebrum and terminate in the corpora cardiaca (CC) of their side. Below the aorta, but dorsal to the oesophagus, lie two oval or spherical corpora cardiaca. A corpus allatum (CA) lies posterior to the corpora cardiaca (CC). The corpora cardiaca do not contain NSM; only the intrinsic secretion of their cells has been occasionally observed which stains orange or green with PF staining method. The corpus allatum sometimes exhibits PF positive granules of cerebral origin. A new connection between the corpus allatum and aorta has been recorded. The suboesophageal ganglion contains two neurosecretory cells of A-type which, in structure and staining behaviour, are similar to the medial neurosecretory cells of the brain. The course and termination of axons of suboesophageal ganglion neurosecretory cells, and the storage organ for the secretion of these cells have been reported. It is suggested that the aortic wall and NCC-I axons function as neurohaemal organ for cerebral and suboesophageal secretions.

Notizen: Pyroantimonate precipitate indicates that the epithelium of the proximal tubule is the only segment of the tubular nephron of the fresh water lamprey where large accumlations of cations are distributed. Unusually large amounts of reaction product are located within the lateral intercellular spaces and within vesicles closely associated with the plasma membrane at the lateral and basal surfaces. This technique suggests the continuity of these vesicles with the plasma membrane and alludes to the possibility of an endomembranous system of vesicles and the intercellular spaces as vehicles for ion transport. Lateral intercellular spaces of proximal tubules of lower vertebrates may play a different role in kidney function that their counterparts in higher vertebrates.Osmium-zinc iodide has a specificity for certain cells within the proximal, intermediate, and distal segments, but no structural differences are noted when these cells are compared to unstained cells. Smooth endoplasmic reticulum remains unstained in the distal segment but the stain has a strong affinity for elements of the Golgi apparatus, lysosomes, and the nuclear envelope of all cell types. This technique does not suggest a structural or functional similarity between cells of the distal segment and the chloride cells of the gills of teleosts.

Notizen: Anatomical analysis of the forebrain and midbrain of Anelytropsis, Dibamus and feyliniids reveals structural similarities with those of skinks and snakes. Skinks and feyliniids are probably derived from a common ancestral stock. This is suggested by mutual reduction of several telencephalic nuclei, by similar trends in the development of the dorsal thalamus, and by similarities in the lamination of their optic tecta. Anelytropsis, Dibamus, feyliniids and snakes show interdigitation of the periventricular gray zones of the optic tectum and enlargement of lamina 7 of the posterior colliculus. Of these three taxa, Dibamus is most similar to burrowing snakes and many of its brain characters are intermediate between skinks and burrowing snakes. These similarities may suggest common ancestry between Dibamus and snakes rather than parallelism.

Notizen: It is possible to monitor the electrical activity of the motor neurons of Drosophila by recording the electrical activity of the muscle fibers. We have found that it is possible to specify the location of the subcuticular terminations and to describe the orientation within the thorax for the individual muscle fibers, because of the large size of the fibers and because the surface anatomy of Drosophila is known in detail. A map has been made to indicate the location of the muscle fibers with respect to superficial landmarks. The importance of the stereotaxic map for physiological studies is discussed.

Notizen: The functional anatomy of pulmonary ventilation in Thamnophis elegans was studied by electromyography. Flow of air into and out of the lungs follows a triphasic pattern and occurs while the glottis is held open by a dilator muscle. Non-ventilatory rest periods characterized by a closed glottis and lack of ventilatory movements occur between breaths. Exhalation is caused by contraction of a pair of dorsolateral sheets of muscle that extends from the ventral surface of the vertebral column to the medial surfaces of the ribs and a pair of ventro-lateral sheets that extends from the medial surfaces of the ribs to the mid-ventral skin. Inspiration is powered by contraction of a series of rib levators and retractors. The last phase of the ventilatory cycle is a passive expiration that may be caused by elastic recoil of the walls of the filled lungs and relaxation of muscles used during inspiration. The site of respiratory pumping is shifted craniad after large prey items have been completely ingested. The significance of this shift and its anatomical basis are considered.

Notizen: As seen in transverse section, doublet elements of the axial unit of spermatozoa of Haematolocchus medioplexus, a frog lung-fluke, possess walls made up of protofibrillar subunits 50-60 Å in diameter. The partition between A and B members of a doublet element often show extra protofibrils which may partially occlude the “lumen” of the A tubule. Each A tubule possesses outer and inner lateral arms which repeat at longitudinal intervals of about 215 Å and which appear to be structurally dissimilar; the outer arm is expanded at its free end and the inner arm often connects to the B tubule of the adjacent doublet element. Regularly-spaced radial links connect the central sheath of an inner core complex to the A tubules of the peripheral doublet elements. Tests for magnesium-activated ATPase activity provide evidence that the enzyme is associated with the surfaces of doublet elements and the surface of the central sheath. Finally, study of an axial unit which developed in an abnormal manner suggests that normal differentiation of an axial unit may depend on the elaboration of a core complex and radial links.

Notizen: This is the first demonstration of an apparent acrosome reaction by the use of negative staining (phosphotungstic acid) and electron microscopy. It is also the first report of such a reaction in spermatozoa of an oligochaete annelid (Lumbricus terrestris). The morphology of the negatively stained unreacted acrosomal complexes is entirely comparable to that seen in sectioned material. After reaction, a short straight filament is extruded and the compartmentalization seen in unreacted spermatozoa is no longer visible. In the flagellar axoneme there are short cross-bridges linking the two central singlet microtubules at 150-170 Å intervals. Two fibrous elements are also present, forming, with the singlets, a tetragon. All four of these structures apparently change their elastic properties after incubation in distilled water for two hours, so that instead of following the doublet microtubules in gentle coils, the central complex components fall as a unit in jagged configurations.

Notizen: Serial sections of embryonic rat eyes were stained with hematoxylin and eosin, quantified (by counting pycnotic and viable nuclei), reproduced by camera lucida on wax plates, and moulded into reconstructions in order to study the normal progression of cellular death during morphogenesis. At least nine distinct necrotic loci (A through I) can be distinguished. Immediately following contact between the retina and surface ectoderm (day 11) degenerating cells were observed in (A) the ventral extent of the optic vesicle, beginning in the mid-retinal primordium and continuing ventrally in the optic stalk, (B) in the rostral optic stalk base, and (C) in the surface ectoderm encircling the early lens placode. No degeneration was observed in the dorsal half of the presumptive retina, in the entire pigment epithelium, or in the lens placode proper. During day 11.5 the lens placode thickens and forms a degenerating locus (D) in its ventral portion opposite the underlying pycnotic zone in the retina (A). During day 12 the ventral pycnotic zone (A) divides into two subunits (A1 and A2). Invagination of the lens displaces its marginal and ventral components (C and D) so that they come to occupy the lens pore area and presumptive corneal epithelium. Simultaneous invagination of the retinal rudiment juxtaposes the pigment epithelium which concurrently forms a necrotic area (E) adjacent ventrally to that in the retina (A1). Degeneration appears in the caudal optic stalk (I). The density of viable cells decreases adjacent to pycnotic areas in the retina and pigment epithelium and increases within these death centers. During day 13 the optic fissure forms within the subunits of the ventral pycnotic zone (A1 and A2). Degenerations are seen in the dorsal optic stalk (F) and in the walls of the optic fissure (G and H). Throughout these stages necrosis appears only in those portions of the eye rudiment where invagination is either retarded or completely absent.In part, these observations suggest that cell death serves (1) to retard or inhibit invagination within death centers, (2) to integrate the series of invaginations which mould the dorsal optic cup and optic fissure, (3) to assist formation of the pigment epithelium monolayer, and (4) to orient the lens vesicle within the eye cup. The spatio-temporal relationship between necrotic loci suggests that pycnotic cells in the retina may influence their production in the lens and pigment epithelium. Preliminary observations on the mouse, pig, and human substantiate those on the rat.

Notizen: The ultrastructural features of cardiac muscle cells and their innervation were examined in the tarantula spider Eurypelma marxi Simon. The cells are transversely striated and have an A band length of about three microns. H zones are indistinct and M lines are absent. Thick and thin myofilament diameters are approximately 200 and 70 Å respectively. Eight to 12 thin filaments usually surround each thick one. Accumulations of thick and thin myofilaments occur perpendicular to the bulk of the myofilaments in some cells. The Z line is discontinuous and thick filaments may pass through the spaces in the Z line. Extensive systems of sarcoplasmic reticulum and transverse tubules are present; these form numerous dyadic junctions in both A and I band regions. Sarcolemmal invaginations form Z line tubules; lateral extensions of the plasma membrane portion of these invaginations form dyads. Nerve branches of the cardiac ganglion make multiple neuromuscular synapses with at least some of the cardiac muscle cells. Both large granular and small agranular vesicles are present in the presynaptic terminals. Intercalated discs similar to those present in other arthropod hearts occur between the ends of adjacent cardiac muscle cells.

Notizen: A cinematographic analysis of the unrestrained walking, trotting, galloping, jumping and landing movements of 11 adult cats was undertaken to provide previously unavailable information concerning the demands imposed on the nervous system for the control of low and high speed movements and the demands imposed by such natural movements on muscle performance and proprioceptive response.With due regard for the swing (F and E1) and stance (E2 and E3) phases of the step cycle of an individual limb, single frame analysis of the film permitted measurement of instantaneous angles of the lower spine, hip, knee, ankle and metatarsophalangeal joints. Appropriate lever arm measurements were also made on 50 freshly dispatched cats and 25 cadavers such that the Law of Cosines could be used to calculate instantaneous lengths of select hind limb muscles that would apply to the natural movements of adult cats of small (1.5-2.5 Kg), intermediate (2.6-3.5 Kg) and large (3.6-4.5 Kg) size. Muscle displacements were analyzed relative to maximum and minimus in situ lengths and the lengths associated with quiet standing. Use was also made of a previous electromyographic analysis of hind limb muscles during unrestrained locomotion (Engberg and Lundberg, '69).The sequential relations between the four phases of the step cycle are maintained as forward speed increases from walking ( 〈 2 mph) to high speed galloping ( 〉 16 mph). There are significant differences in the time consumed by each phase, however, with a greater reduction in the E3 phase, little reduction in the E2 and E1 phases and virtually no reduction in the F phase. When each phase is expressed as a relative percentage of the duration of the total step cycle, the greatest reduction is again in E3 with little change in the E2 phase. In contrast F and E1 phases increase in the percent of time they occur in each cycle, with the greatest increase in the F phase. For all speeds, analysis of the phase relations between movements of various sections of the hind limb revealed a remarkable unity of knee and ankle joint movement. The hip joint is largely out of phase with the knee and ankle during E1 and E2, all three joints being in phase in F and E3. The digits are essentially out of phase with the other joints except in the stance phase of the gallop.Rates and extents of muscle displacement during natural movements are greater than might be anticipated when expressed in absolute mm's and mm/sec but not when considered in relation to maximum and minimum in situ length and the length associated with quiet standing (Ls). During stepping a progressive increase in forward speed results in: (a) a greater usage of muscles at lengths between Ls and maximum in situ length; (b) for knee and ankle extensors, pronounced increase in the lengthening contraction associated with the E2 (yield) phase of step; and, (c) for both flexor and extensor muscles, an increased active phase of lengthening or near isometric contraction immediately prior to periods of active shortening. In contrast to these changes in active muscle status, the change from walking to galloping has little effect on the extent and rate of passive muscle displacements, particularly the F phase stretch of extensors.For the soleus muscle, calculations were made of the relation between changes in overall muscle length during natural movements and the length of the average muscle fiber and the tendon of insertion. These measurements revealed that the increases in fiber length when passive and decreases in length during active shortening are less than would be anticipated from the extensive liteature on extirpated fibers. In contrast, the increase in fiber length when active is greater than would be expected from the admittedly sparse literature on this subject.The results of this study are discussed largely in relation to two points of neurophysiological interest: the physiological range of muscle stretch as it pertains to the responsiveness of muscle spindles and tendon organs; and those mechanical aspects of lengthening contractions that give insight into the neural control of stepping. For exciting both spindles and tendon organs passive muscle stretch and shortening contractions are shown to be relatively ineffective and lengthening and isometric contractions particularly effective movements. It is suggested that, just as recent literature has emphasized the co-activation of efferent alpha and gamma motoneurons as a muscle becomes active, so too is there a synchronous activation of afferents, particularly the Ia and group II endings of muscle spindles and Ib endings of tendon organs. Finally the thesis is advanced that, while it has been convenient to separate E2 from E3 in the description of the stance phase of the step cycle, extensor muscles are actually undergoing a single mechanical event: an active stretch-shorten cycle for knee and ankle extensors and an active isometric-shorten cycle for hip extensors. This hypothesis has significant implications for the neural control program that regulates the stepping sequence in that it emphasizes the extent to which appropriate changes must be preprogrammed in the mechanical properties of muscles for the smooth execution of stepping.

Notizen: Cytological and cytochemical methods were used to identify and characterzie six distinct regions of the crayfish kidney: coelomosac, labyrinth I and II, and nephridial canal I, II, and III. Cells of the coelomosac possess cytoplasm which is strongly PAS-positive, but poor in RNA and protein. Their nuclei possess unusual projections which extend to the basal plasmalemma. Labyrinth I contains columnar cells rich in glycogen. Labyrinth II is characterized by a distended lumen and by shorter cells with high cytoplasmic RNA, many possessing a large intracellular vacuole. A PAS-positive brush border is unique to the two portions of the labyrinth. Cells in the nephridial canal show strong reactions for RNA and Mg++-dependent ATPase. In nephridial canal I and II, cells are flattened to cuboidal with the lumen being more distended in nephridial canal I than anywhere else in the tubule. In nephridial canal III, the cells are large and columnar, and the cytoplasmic RNA concentration is greatest apically. Nuclei in all regions of the tubule epithelium, except coelomosac, are large and react strongly for protein. Coelomosac nuclei and those in blood cells are condensed and contain little protein. The cytoplasm of blood cells displays a significant amount of RNA, and traces of polysaccharide material.These observations demonstrate the presence of highly specialized morphological and histochemical alterations along the length of the kidney tubule and indicate sequential modification of urine in the lumen. Evident morphological and cytochemical likenesses between analogous regions of the mammlian nephron and the crayfish kidney tubule suggest that basic physiological similarities may also exist.

Notizen: In the tiger salamnder the distribution of optic fibers, as revealed by the Fink-Heimer method, is compared with the localization of acetylcholinesterase, as revealed by histochemical methods. AChE activity coincides with optic nerve axons in the optic fiber layer of the retina, in the optic nerve, in the optic tracts and in every optic projection. Reginons of optic fiber terminals show heavier activity than optic fibers of passage. Comparison with other vertebrates is also made.

Notizen: Early descriptions of insect sensory organs included three presumed mechanotransducers in the tibia of Orthoptera, namely the subgenual organ, the intermediate organ, and the tympanal organ. This investigation re-evaluates the light microscopic appearances of these organs in the foreleg tibia of the cricket, Gryllus assimilis, initially described by Herbig in 1902.The study also examines the fine structure of the subgenual and intermediate organs and provides the first fine structure analysis of these structures.The subgenual and intermediate organs are typical scolopophorus organs suspended perpendicular to each other within the dorsal hemolymph canal. Each is innervated by dendrites from the anterior ganglion. Neither the subgenual, intermediate, nor tympanal organ is structurally related to the larger posterior tympanic membrane.The study shows that the tibial tympanal organ in the cricket is not a scolopophorus organ, but consists of highly modified epithelium, associated with the anterior tympanic membrane, and receiving innervation from the anterior ganglion.

Notizen: The development of the electric organs of Gymnarchus niloticus has been studied and the origin and histogenesis of an electroplate worked out. A segmental origin of the electroplate is reported for the first time for this fish. Light has been thrown on many hitherto obscure phenomena, viz., growth of core girth, loss of transverse striations on the myofibrillar elements, differentiation of electroplate polarities, shortening in length of the electroplate etc. The transverse striations of the myofibrillar bundle of the electroplate primordium progressively disappear with development owing to splitting apart of the constituent myofilaments and consequent loss of their parallel order, and not to degeneration of the myofibrillar bundle. The excessive growth of the core girth of the electroplates is caused by the deposition of some kind of interfibrillar substance probably secreted by the peripheral cytoplasm.

Notizen: The structure of the caudal muscle in the tadpole larva of the compound ascidian Distaplia occidentalis has been investigated with light and electron microscopy. The two muscle bands are composed of about 1500 flattened cells arranged in longitudinal rows between the epidermis and the notochord. The muscle cells are mononucleate and contain numerous mitochondria, a small Golgi apparatus, lysosomes, proteid-yolk inclusions, and large amounts of glycogen. The myofibrils and sarcoplasmic reticulum are confined to the peripheral sarcoplasm.Myofibrils are discrete along most of their length but branch near the tapered ends of the muscle cell, producing a Felderstruktur. The myofibrils originate and terminate at specialized intercellular junctional complexes. These myomuscular junctions are normal to the primary axes of the myofibrils and resemble the intercalated disks of vertebrate cardiac muscle. The myofibrils insert at the myomuscular junction near the level of a Z-line. Thin filaments (presumably actin) extend from the terminal Z-line and make contact with the sarcolemma. These thin filaments frequently appear to be continuous with filaments in the extracellular junctional space, but other evidence suggests that the extracellular filaments are not myofilaments.A T-system is absent, but numerous peripheral couplings between the sarcolemma and cisternae of the sarcoplasmic reticulum (SR) are present on all cell surfaces. Cisternae coupled to the sarcolemma are continuous with transverse components of SR which encircle the myofibrils at each I-band and H-band. The transverse component over the I-band consists of anastomosing tubules applied as a single layer to the surface of the myofibril. The transverse component over the H-band is also composed of anastomosing tubules, but the myofibrils are invested by a double or triple layer. Two or three tubules of sarcoplasmic reticulum interconnect consecutive transverse components.Each muscle band is surrounded by a thin external lamina. The external lamina does not parallel the irregular cell contours nor does it penetrate the extracellular space between cells. In contracted muscle, the sarcolemmata at the epidermal and notochordal boundaries indent to the level of each Z-line, and peripheral couplings are located at the base of the indentations. The external lamina and basal lamina of the epidermis are displaced toward the indentations.The location, function, and neuromuscular junctions of larval ascidian caudal muscle are similar to vertebrate somatic striated muscle. Other attributes, including the mononucleate condition, transverse myomuscular junctions, prolific gap junctions, active Golgi apparatus, and incomplete nervous innervation are characteristic of vertebrate cardiac muscle cells.

Notizen: The pharynx, intestine and respiratory duct of Xenopus laevis were examined by light and electron microscopy, at different stages of the metamorphic cycle, through climax.It is well known that preclimactic larvae are suspension feeders and that after climax specimens feed on solid food. It is shown that the histology of the pharynx and the alimentary canal changes in adaptation to the change in the mode of feeding.Suspension feeding utilises ciliary activity but after climax cilia have disappeared from the pharynx and alimentary canal, when new neuromuscular mechanisms are utilised in feeding.Other morpho-histological changes in various intestinal and respiratory tissues are likewise considered in terms of functional activity.

Notizen: The scanning electron micrographs show the external morphology of the maxillae of Drosophila melanogaster. Specifically, they illustrate the patterning of the different types of chemo-receptive sensilla on the maxillary palpi making possible a clearer understanding of the structure of the tiny maxillary lobes. It appears that the maxillary lobes act as “cleaning brushes” during the feeding process.

Notizen: A cephalic organ of presumed sensory function is described in nauplii and copepodids of the ascidicolous copepod Doropygus seclusus Illg. The receptor, located bilaterally in the anterodorsal head region, is composed of dendrites of extra optic protocerebral origin which have ciliary protrusions with basal bodies, no rootlets, and a basal infrastructure of the 9 + 0 type. The cilia do not branch and their distal terminations contain only one to four microtubules. In nauplii and free-living copepodids, a large epidermal supporting cell encapsulates the end of one dendrite and its cilia in a sac. Other dendrites and their cilia pass through the supporting cell and, terminally, the cilia escape to form a whorled fascicle which contacts the anterolateral cephalic cuticle. The latter end organ reaches its greatest development in the second copepodid stage  -  the stage which infects the ascidian. All of the symbiotic stages of the copepod have only a proportionately smaller end organ of the saccular type and apparently lack the end organ consisting of whorls of ciliary ends. The function of the receptor is unknown, but it is suggested that the end organ which disappears in the symbiotic stages functions in second copepodids in host recognition.

Notizen: The spleen of the adult gerbil (M. unguiculatus) is characterized by the absence of venous sinuses and ellipsoid sheaths. The follicle (white pulp) is separated from the surrounding red pulp by a distinct marginal zone. The cell types in the marginal zone are common to both the follicle and red pulp. Separating the marginal zone from the follicle is a vascular channel of capillary dimension, the marginal sinus. A number of terminal segments of the arterial vessels within the follicle were observed to form a direct connection with the marginal sinus. Ultrastructurally, discontinuities were evident within the walls of the marginal sinus that would permit passage of both cellular and plasma components from the marginal sinus to either marginal zone or the follicle.

Notizen: The innervation of each of the muscles involved in mediating head movement in the desert locust Schistocerca gregaria is described in detail. The number of motor neurones to each muscle and the neutral pathway and ganglion of origin of each are deduced from both histological and electrophysiological evidence. Only two of the muscles are, on histological evidence, innervated by as few as four different neurones, while several receive more than ten, and one at least 13. Individual muscles are shown physiologically to receive, in a few cases, as many as six different motor neurones. At least six muscles are innervated by motor neurones originating in more than one ganglion. One group of four muscles consisting in total of less than 100 muscle fibres receives more than 20 different motor neurones from three different ganglia through three or four different nerve roots. In these muscles, many single muscle fibres receive innervation from at least two different ganglia. It is concluded that the segmental nature of an insect muscle can not be deduced solely from a knowledge of the ganglion of origin of the motor innervation to that muscle. The innervation patterns that exist today must reflect past evolutionary development, but changes in the peripheral distribution of motor neurones, or migration of motor neurone cell bodies from one ganglion to another, or the development of additional motor neurones, or several of these factors together, must have formed a part of that development.

Notizen: 1. Forty-eight species of oribatids in 37 families representing most of the superfamilies were collected from various environments (littoral, salt marsh, litter, sod, and freshwater) and sectioned.2. The coxal gland is composed of a sacculus and a labyrinth in all stages of all oribatid species. Muscles, originating on the body wall, insert at several points on the thin-walled sacculus which opens into the labyrinth. The labyrinth has an internal, chitinous supporting skeleton. The type A labyrinth has 3-180° bends, producing four parallel regions, and occurs in all inferior oribatids. The type B labyrinth has 1-180° bend, producing two parallel regions, and occurs in all superior oribatids. The coxal gland duct and the lateral gland duct join, penetrate the body wall, and empty into the posterior end of the podocephalic canal. All oribatids have lateral accessory glands, but only inferior oribatids have rostral and medial glands. Three ductless coxendral bodies are always present.3. The labyrinth length in oribatids is correlated with body size and the environment of the species. Oribatids from sod, leaflitter, or moss show a simple correlation of labyrinth length (X) to total body length (Y) where Y = 4.64X. Freshwater species have a labyrinth length greater than that of comparably sized terrestrial species and salt water (littoral) species have a labyrinth length less than that of comparably sized terrestrial species. There is a greater reduction in labyrinth length in species restricted to salt marshes than in species not restricted to salt marshes.4. The probable function of oribatid coxal glands is osmoregulation. Hemolymph filtration would occur across the sacculus by positive hemolymph pressure and contraction of the sacculus muscles. Resorption of ions would occur in the labyrinth, which is noncollapsible due to the internal skeleton. The hypothesis is that in freshwater species the rate of filtration is high and resorption of ions would have to be very efficient, therefore they have an elongated labyrinth; but in salt water species water loss must be minimized and preservation of ions would be a disadvantage, therefore they have a shortened labyrinth. Excre ion may also be a function of the coxal glands. The lateral gland may possibly function as an endocrine gland involved with production of a molting hormone. The rostral glands in inferior oribatids may have a salivary function.5. The coxal glands of Peripatus, some millipedes, apterygote insects, decapod crustaceans, and all arachnid orders are homologous. The Tetrastigmata, Notostigmata, Cryptostigmata, and soft ticks have typical arachnid coxal glands. The coxal glands of higher Prostigmata may be modified into salivary, silk, or venom glands. The coxal glands in Mesostigmata, Astigmata, and hard ticks are lacking or highly modified.

Notizen: The blood system of the flabelligerid polychaete, Flabelliderma commensalis has been explored by dissection, light and electron microscopy and absorption spectrophotometry. The main longitudinal vessels are the dorsal, ventral, perineural, sub-oesophageal, supra-oesophageal and heart. Each segment has a segmental vessel which communicates with the dorsal vessel in thoracic setigers and the gut sinus in abdominal setigers. Branches of the segmental vessels in setigers 2-9 supply the gonads. A blood sinus envelopes most of the gut. Circulation is maintained by the pumping of the heart which immediately supplies blood to the supra-oesophageal ganglion, the branchiae and the palps. These are paralleled by a system of collecting vessels. The sinus of the supra-oesophageal ganglion receives a number of different axonal endings, some of which may be neurosecretory. The retroperitoneal vessels in their most developed form are composed of an intima, longitudinal and circular muscles and a peritoneum. The heart vessel contains a cardiac body whose cells appear to contain vacuoles of blood pigment. The blood pigment exhibits the absorption characteristics of a chlorocruorin with maxima at 438, 558 and 606 nm.

Notizen: Attachment of muscle of the integument was studied in two species of Balanidae, Balanus balanoides and B. improvisus with electron microscopy. Specilalized epithelial cells (tendon cells) intervene between the muscle and overlying cuticle. An extensive desmosome-like junction exists between these two tissues. The tendon cell contains huge amounts of microtubules aligned parallel to the long axis of the inserting muscle. Tension exerted by contracting muscles is conveyed to the chitinous exoskeleton via the specially organized tendon cells and the extensive myo-tendinal cell junctions.

Notizen: Among ants, Cataglyphis bicolor shows the best performance in optical orientation. Its eye is of the apposition type with a fused rhabdom. Morphological studies on the general struture of the eye as well as the effect of light have been carried out with transmission and scanning electron microscopy.An ommatidium is composed of a dioptric apparatus, consisting of a cornea, corneal process and a crystalline cone, the sensory retinula, which is made up of eight retinula cells in the distal half and of an additional ninth one in the proximal half. The ommatidia are separated from each other by two primary pigment cells, which surround the crystalline cone and an average of 12 secondary pigment cells, which reach from cornea to the basement membrane.The eye of Cataglyphis bicolor possesses a light intensity dependent adaptation mechanism, which causes a radial and distal movement of the pigment granules within the retinula cells and a dilatation of cisternae of the ER along the rhabdom.Until now, no overall order in arrangement of retinula cells or direction of microvilli has been found from ommatidium to ommatidium. Such an order, however, must exist, either on the retina or the lamina level, since we have proven the ant's capacity for polarized light analysis.

Notizen: The ultrastructure of wing epidermis of the giant silkmoth, Hyalophora cecropia, was studied during pupal diapause and the first half of development to the adult. In diapause, the generalized epidermal cells are characterized by many free ribosomes, some vesicles and small lamellae of rough endoplasmic reticulum, some scattered short mitochondria and a few small Golgi complexes. During the early states of post-diapause development, before and after the time of apolysis (separation of the epidermis from the overlying cuticle), there is a marked increase in structures often associated with synthetic functions, such as polyribosomes, lamellate rough endoplasmic reticulum and Golgi complexes. On day five of post-apolysis development, just after the appearance of scale-forming and socket-forming cells, the generalized epidermal cells lay down the cuticulin layer of the adult cuticle. At this stage and later, the polyribosomes and lamellate rough endoplasmic reticulum decrease in abundance. Cell nuclei show three phases of temporary transition from predominantly lobed to predominantly round profile, which correspond to periods of reported DNA synthesis. Throughout this developmental process, therefore, there is good correlation of fine structure with changes in macromolecular synthesis recorded elsewhere.

Notizen: The circulatory system of Pollicipes polymerus exhibits a high degree of organization which precludes it from being referred to as an open system. The system is arbitrarily divided into four parts: (1) the circulation of the peduncle and mantle; (2) the distributive circulation of the body, which provides hemolymph to most of the cephalic gut, to the maxillary gland, and to the cirri; (3) the peripheral circulation which distributes blood from the cirri to the peripheral areas of the thoracic region, to most of the thoracic gut, and from the scutal sinus to the peripheral areas of the cephalic region; and (4) the collecting circulation, which conveys hemolymph mostly from the peripheral circulation of the body to the peduncle. There also may be a circulation that is comparable to the vertebrate lymphatic system.Pumping of hemolymph can be attributed to three pairs of skeletal muscles that compress the dorsolateral channels. These muscles are unique for crustacean muscles in that they do not appear to be striated.The rostral vessel appears to be a vestige of a heart in which the pump muscles have been lost. There is a similarity of the rostral vessel to the heart of Calanus finmarchicus (a copepod). This is additional evidence linking the cirripeds with the copepods within the Maxillopoda.Electron microscope observations of the walls of the midsagittal vessels indicate that there is a more or less random layering of cellular and noncellular elements within the wall. Muscle cells appear to be incorporated in the vessel wall.

Notizen: Oogenesis in the anuran Xenopus laevis can be divided into six stages based on the anatomy of the developing oocyte. Stage I consists of small (50 to 100 μ) colorless oocytes whose cytoplasm is transparent. Their large nuclei and mitochondrial masses are clearly visible in the intact oocyte. Stage II oocytes range up to 450 μ in diameter, and appear white and opaque. Stage I and II are both previtellogenic. Pigment synthesis and yolk accumulation (vitellogenesis) begins during Stage III. Vitellogenesis continues through Stage IV (600 to 1000 μ), the oocytes grow rapidly, and the animal and vegetal hemispheres become differentiated. By Stage V (1000 to 1200 μ) the oocytes have nearly reached their maximum size and yolk accumulation gradually ceases. Stage VI oocytes are characterized by the appearance of an essentially unpigmented equatorial band. They range in size from 1200 to 1300 μ, are postivtellogenic and ready for ovulation. These stages of oocyte development have been correlated with physiological and biochemical data related to oogenesis in Xenopus.

Notizen: The ultrastructure of the epidermis at different stages of the shedding cycle has been studied in Anolis carolinensis. Cells of the germinal layer are morphologically similar at all stages in the cycle. Immediately after leaving the germinal layer all daughter cells resemble one another closely. However, they later acquire specific ultrastructural features that enable them to be classified into six distinct fully differentiated types corresponding to the grouping previously set forth by light microscopy. A comparison of cytoplasmic filament size with the known X-ray diffraction data suggests that the Oberhautchen and β-layer contain a protein similar to that of avian feather; the protein in the α-layer and lacunar tissue is similar to that in mammalian hair, and the mesos layer cells probably contain a mixture of feather and hair-like proteins. The nature of the amorphous cytoplasmic material in the mature clear layer is as yet unknown.

Notizen: The interspecific variation in the positional and mesenteric relationship of the mammalian oviduct to the ovary observed among 41 species is summarized by distinguishing eight morphological types of relationship. The recognition of types is based on wide species differences in: the position of the oviduct with reference to the mesosalpinxal fold and ovary; the extent to which oviducal mesenteries enclose the ovary in a periovarial sac; the degree of closure and method of formation of the peritoneal opening to the periovarial sac; and the morphology of the oviduct.

Notizen: A study of the integument of the aquatic mite Arrenurus major Marshall is presented. When the cuticle is examined with the unaided eye and the light microscope, it appears to possess numerous tiny pits. However, scanning electron micrographs of the cuticle reveal that it is a solid surface with topographical sculpturing of the epicuticle, indicating that the “pits” are an internal phenomenon. In cuticle which has been sectioned, areas devoid of cuticular material beneath the thin exocuticle are revealed. These areas are the pits which are goblet-shaped.The integument consists of five major strata. These are from the outside to the inside: (1) a superficial layer with a maximum observed thickness of 725 Å, (2) an epicuticle with a thickness of about 900 Å and composed of at least four sublayers, (3) an exocuticle with a thickness of about 1.5 Å. Fibers of the exocuticle are arranged in a Bouligand pattern and exhibit a regularly occurring discontinuity with a spacing of 200 Å. (4) An endocuticle ranging from 15 to 20 μ in thickness. The endocuticle is characterized by bandings which superficially resemble the lamellae of insects but are not homologous, microfibers which exhibit a preferred orientation, and the presence of the pits; and (5) an epidermis lying beneath the endocuticle and extending into the pits.Pore canals are present only in the exocuticle and have their origin at the apices of the pits. The pore canals contain a central filament, and a plug is present just beneath the epicuticle.

Notizen: This report presents light microscopic descriptions of lymphoid organs and aggregates in the snapping turtle Chelydra serpentina. The thymus and spleen were found to be similar to those of other ectothermic vertebrates. Certain gut associated lymphoid aggregates suggest the presence of reptilian equivalents of tonsils, Peyer's patches and the avian bursa of Fabricius. Lymphoid aggregates located in the axillary and inguinal regions were apparent for the first time in an ectothermic vertebrate. These are of particular interest since they may represent ancestors of true lymph nodes in analogous locations in mammals. It is concluded that the snapping turtle is not deficient in lymphoid tissue, although there is a conspicuous absence of typical germinal centers, characteristic of mammalian organs.

Notizen: One hundred and twenty-two larvae of Xenopus laevis, the South African clawed toad, at developmental stages 48, 50, 52 and 54, were implanted in the tail with two allografts from adult tissues. In each case, one allograft was from kidney, while the other was either from kidney, thymus, spleen, or liver. In any particular host the two implants were always from the same donor and the implants were all visually matched in size. The experimental period was a maximum of nine days, so as to minimize the large numbers of changes normally accompanying larval progress from stage to stage. We are concerned with the timing of allograft response initiation under the implant conditions of each experimental group at a particular point in development. An allograft response was defined as an infiltration and accumulation of small lymphocytes in the “test” kidney allograft. Larvae of all stages developed allograft responses within one week post-implantation when the variable implant was from kidney, but implants from spleen and thymus suppressed both the timing of initiation and the subsequent intensity of the response. Spleen was more effective in this regard than thymus and both were more effective in the earlier larval stages. Liver proved to be toxic to the larvae. The relationship between the maturation of the lymphomyeloid tissues and external morphological staging is also discussed.

Notizen: The midgut epithelium of larval and early postlarval brown shrimp has been studied with light and electron microscopy. Ultrastructurally the features of the midgut do not change during these stages of development. On the basis of electron density, two epithelial cell types can be distinguished, and these are referred to as light and dark cells. The dark cells contain more rough endoplasmic reticulum and more free ribosomes than the light cells. Mitochondria in the dark cells have a matrix which is less electron dense than the mitochondrial matrix of the light cells. Both cell types have a microvillous border with a surface coat. The microvilli lack microfilaments within their core, and a terminal web is not differentiated in the stages examined. Tubular smooth endoplasmic reticulum is abundant in the basal portions of the cells. Electron dense, membrane bound vesicles are consistently seen in association with the Golgi apparatus, apical cell surface, and gut lumen and therefore are believed to be secretory granules. Cells in the anterior portion of the midgut often contain very large lipid droplets in the cytoplasm.

Notizen: The hamster nasal cavity consists of vestibular, non-olfactory and olfactory portions. Much of the non-olfactory nasal cavity surface is lined by cuboidal, stratified cuboidal, and low columnar epithelia, devoid of cilia. Goblet cells and ciliated respiratory epithelium are present over only a small portion of the nasal cavity surface.The largest glandular masses in the hamster nose are the maxillary recess glands, the vomeronasal glands and the lateral nasal gland 1; these three glands contain neutral mucopolysaccharides (PAS-positive). Other nasal glands contain both acidic and neutral mucopolysaccharides; the staining reaction for acidic mucopolysaccharide is stronger in goblet cells and olfactory glands than in the other nasal glands.The ducts which open into the nasal vestibule are the excretory ducts of compound tubuloacinar serous glands. The one major PAS-positive gland whose duct opens into the nasal vestibule is the lateral nasal gland 1. The ducts of the compound tubuloacinar vomeronasal glands open into the lumen of the vomeronasal organ, which is connected to the ventral nasal meatus by means of the vomeronasal duct. The ducts of the branched tubuloacinar maxillary recess glands open into the maxillary recess. Few ducts open into the caudal half of the nasal cavity.

Notizen: A differentiated segment, analogous in location and structure to the first portion of the sexual segment of the males, but much smaller, is observed in the renal collecting ducts of female C. lemniscatus. In addition to this first portion, with cells full of granules strongly positive to periodic acidleucofuchsin, males have a consecutive second portion, with granules localized only in the apical part of the cells, moderately positive to the reaction mentioned and with a marked affinity for orange G. The two portions of the male sexual segment are considered to correspond to the middle and final parts of the collecting ducts; the initial part in both sexes and the final one in the female are mucigenous.

Notizen: Regional variation in the vertebral column of several species of salamanders (families Ambystomatidae, Salamandridae and Plethodontidae) is analyzed. Measurements of three dimensions, centrum length, prezygapophyseal width, and transverse process length, provide the data. Ontogenetic, interspecific, intergeneric and interfamilial patterns of positional variation are diagrammed and discussed. Distinctive patterns of variation characterize the families, genera, and to a lesser extent, the species. The patterns of ambystomatid salamanders are the most generalized, and probably reflect derivation from a primitive ancestral stock. The most specialized conditions occur in the fully terrestrial plethodontids, a group generally considered to be highly derived. Data such as those presented here will aid in the identification of fossils.The patterns described have functional significance. For example, species which have an aquatic larval stage and which return to aquatic breeding sites have vertebrae which taper in length and width behind the pelvis. This is a feature associated with production of a traveling wave in the tail which is necessary for propulsion in water. Fully terrestrial species do not have a tapering column. In them, standing waves, such as occur in the trunk region of all species, typically occur in the tail. The caudal vertebrae of terrestrial species are rather uniform in dimensions for some distance, and the tail is cylindrical in form. Other functionally important features include the narrowing and shortening of some anterior vertebrae, associated with the development of a neck in some species with tongue feeding mechanisms. In contrast, species which use their heads as wedges during locomotion have broadened anterior vertebrae which serve as sites of origin for hypertrophied neck muscles.

Notizen: The anatomy of the nasal cavities and lateral nasal gland (functioning as a salt gland) are similar in the four species of Acanthodactylus studies. Nasal cavities are not histologically different from those of other squamates. The vestibule is covered with a multilayered, stratified, squamous epithelium. The nasal gland is situated in the conchal space, lateral to the principal cavity and the vestibule. It is a tubular branched gland, highly vascularized. Innervation is derived from the N. trigeminus and was observed to reach only the anterior, small portion of the gland. The collecting duct opens to the vestibule, anterior to its connection to the principal cavity. Secretion of the nasal salt gland probably collects in lower anterior part of the vestibule. From there, liquid can either dry out while moistening the inspired air or be blown out by “sneezing.” Histological differences were observed between a non-active and an active salt gland.

Notizen: Tadpoles of several different genera were fed graded suspensions of uniform polystyrene particles to determine the lower size limit of particles that could be ingested. Certain tadpoles can extract suspended particles as small as 0.126 μ in diameter from the water. In terms of particle size, this is an efficiency comparable to the best mechanical sieves that can currently be produced by man. A mechanism for ultrasplanktonic entrapment is proposed on the basis of scanning electron micrographs of the secretory ridges in the branchial food traps of Rana catesbeiana before and after feeding.Xenopus tadpoles in yeast suspensions modify their clearance and buccal pumping rates in response to varying food concentrations. This may be an adaptation for maintaining a constant input of food mass to the tissues that extract the food from the water.Variability in the lower size limit of filterable particles among tadpoles of different genera correlates with the availability of suspended matter in the microhabitat where these tadpoles may be found.

Notizen: The venom apparatus of the scorpion, C. sculpturatus (Ewing) was studied with light and electron microscopy. Each of the paired glands is lined by secretory epithelium made up of a single layer of columnar cells. Extensive folding in the epithelial layer creates a primitive acinar gland. The secretory products are either membrane-bound or unbound vesicles with discrete morphologies and are observed in the extruded venom, within the lumen of the gland, and within single secretory cells.The venom apparatus, including connective tissues, nerve cells, and muscle tunic is described and correlations are made with observations in other Athropods.

Notizen: The morphology of the rectal pads of two cockroaches, Blattella germanica and Blaberus giganteus is described and contrasted with that of Periplaneta americana, studied previously. The columnar absorptive cells of the three species are similar in structure. However, Blattella and Blaberus rectal pads have a second type of cell, termed the secondary cell, that is not present in Periplaneta. The secondary cells are embedded in the pad epithelium and have crypts of cavities opening into the subepithelial sinus. In addition, a multilayered sheath is present between the pad cells and the sinus. The sheath acts as a barrier, perhaps of low permeability, between the subepithelial sinus and the pads. It is interrupted only at the borders of the secondary cells. A mechanism for fluid absorption is presented and the possible role of secondary cells is discussed. It is proposed that the secondary cells reabsorb solute from the sinus and that this solute can then be recycled through the pad cells. Structures resembling neurosecretory terminals within the cavities of the secondary cells may be involved in regulation of recycling. The arrangement of the rectal pads in these insects has structural and perhaps functional similarities with other transporting systems, particularly the cryptonephric system.

Notizen: Light and electron microscope studies indicate that the old ependyma just proximal to the plane of amputation in early lizard tail regenerates shows a sequence of morphological changes which suggests that it as well as the new ependyma growing into the regenerate may play an active role in the initiation and maintenance of early tail regeneration.The old ependyma close to the plane of amputation undergoes hypertrophy and/or hyperplasia causing a partial closure of the central canal and pseudostratification. Its nuclei shift from an original apical position to a basal one. The ependymal processes become more prominent and extend to the pia, a condition not found more rostrally. There is also a significant increase in the amount of Golgi substance and a moderate increase in the rough endoplasmic reticulum. These observations lead to the thought that these cellular changes may be an expression of enhanced secretion and other activities in the old and new ependyma just proximal or distal to the plane of amputation.

Notizen: Statistical analyses of chromatophore densities and morphological states in wild type, burnsi, and kandiyohi: adult Rana pipiens integument yielded the conclusion that disruptive pigmentary pattern is permanently defined by regional chromatophore densities. Spatial chromatophore patterning is enhanced and rendered more visible by the morphological and physiological differences among chromatophores within the various pattern regions. Specifically, (1) chromatophores were differentialy distributed among pattern regions, (2) greater complexity of gross disruptive patterning had greater underlying melanophores densities, (3) there were significant density differences among non-sib individual animals, among fertilization, and among shipment batches, but not among full-sibs, and (4)kandiyohi individuals had more while burnsi individuals had fewer total melanophores than wild type. A stellate morphology was significantly correlated with high melanophore density, although the relationship of melanophore density to melanophore morphology differed among pattern regions and among genotypes. The functional interrelationships of density and morphology, and their role in disruptive patterning and coloration, are discussed.

Notizen: The male rotifer copulatory organ is composed of a urethral canal extending from the tip of the copulatory organ internally to a layer of microvilli. The microvilli project from two different cell types, referred to as the internal and peripheral microvillar cells according to their location. At this microvillar junction a second canal, the vas deferens, continues posteriorly and enters the sperm duct region of the testis. The channel of the vas deferens is formed from the inner wall of three separate cells; the cap, intermediate and basal cells. Peripheral to these cells and parallel to them for their entire length, cross sections of seven prostate gland cells can be observed. Anteriorly, these gland cells are connected to the basal end of the microvillar layer via a short neck region, through which glandular secretion occurs only during copulation. The mechanism of secretion appears to be a form of exocytosis whereby the secretory granule membrane fuses with the cell plasmalemma so that rupturing at the point of fusion will release the granule content into the neck region.The prostate gland cells contain an abundance of autophagic vacuoles while most of the other cells of the copulatory organ contain primary lysosomes and cytolosomes. These organelles may be associated with the aging process in rotifers, or, as in the case of the prostate gland-autophagic vacuoles, with a fast organelle turnover during secretion.

Notizen: Spermatogonia of the nine-banded armadillo, Dasypus novemcinctus mexicanus, were studied morphologically using light and electron microscopy and examined histochemically using light microscopy. Immature flat type spermatogonia have ovoid or irregular nuclei with loosely condensed chromatin. Free ribosomes are abundant while profiles of rough endoplasmic reticulum are scarce. Smooth endoplasmic reticulum is a prominent feature occasionally taking an unusual cylindrical form. Mature spermatogonia exhibit rounder nuclei with greater degrees of chromatin clumping. Smooth endoplasmic reticulum is no longer prominent whereas profiles of rough endoplasmic reticulum are quite common. Occasional lysosomal configurations are found in mature spermatogonia.The majority of spermatogonial cells exhibit weak to moderate reactivity when stained with the periodic acid-Schiff (PAS) reaction. Certain cells in each tubular cross section stain vividly with this reaction and the PAS positivity is removable with salivary amylase. Because of nuclear characteristics, position of the cell immediately upon the basal lamina, intensity of the PAS reaction and the relative paucity of the vividly staining cells, it is suggested that they are members of the immature spermatogonial cell line, perhaps acting as stem cells. None of the several other histochemical procedures employed was capable of selectively demonstrating these cells.

Notizen: The duodenal glands of four marsupial species, the kangaroo, native cat, marsupial mouse, and bandicoot, form a narrow lobular collar immediately distal to the gastrointestinal junction. In two species, the koala and wombat, the duodenal glands are diffuse and scattered along the intestinal tract distal to the gastrointestinal junction for considerable distances. The glands of all species examined empty independently into the intestinal lumen. Histochemical studies indicate that the latter two species, the koala and wombat, elaborate an acid mucin whereas the former species produce a neutral mucosubstance. Ultrastructural examination shows that generally the duodenal glands are comprised of large pyramidal cells that show a definite polarity, with basally-placed nuclei and apically-situated secretory granules. Species differences, with regard both to the morphology and nature of the secretory granules and to the proportions of cell organelles, exist. The diversity of diet between species is discussed.

Notizen: Cytodifferentiation of the myoepithelial cells (MEC) of the rat submandibular gland (SMG) was observed by studying the prenatal and postnatal development of the gland in vivo and in vitro by light and electron microscopy. The anlage of the SMG first appeared on the fourteenth day of gestation and, from its earliest inception, was surrounded by an intact basal lamina. Presumptive myoepithelial cells were first seen at 18 days of gestation coinciding with the onset of secretion in the rudiment. These cells were flattened, peripherally located and subjacent to the epithelial basal lamina. Initial deposition of cytofilaments in the MEC's was observed during the first three days following birth and fully matured cells were seen as early as one week after birth. Presumptive and immature MEC's were observed undergoing mitosis, but once cytofilament deposition had begun in the cells they did not divide. Myoepithelium developed in relation to embryonic secretory structures and were only observed surounding acini and intercalated ducts in the adult gland. New myoepithelial cells were formed as long as new acinar-intercalated duct units were formed. Myoepithelial cells did not produce secretory type granules at any time during their development or in their mature state.Development of the MEC's in vitro paralleled that in vivo and supported the above observations.

Notizen: Larval compound (jointed) setae of the polychaete Nereis vexillosa Grube were examined by scanning and transmission electron microscopy and by polarization microscopy. Long-bladed spinigers and short-bladed falcigers are described. The proximal shaft of each of these types of setae flares distally into a serrated collar and encloses the proximal end of a toothed blade. The collar projects on one side as a boss. The blade and the cortex of the shaft have longitudinal channels. A large excentric cavity in the shaft (the medullary channel) contains a loose meshwork of trabeculae. In the distal part of the shaft these trabeculae are aggregated into diaphragms. The seta is invested with an electron dense layer of enamel. Juvenile setae contain both chitin and protein. With respect to the long axis of the seta, the blade and the cortex of the shaft are positively birefringent and the medullary diaphragms are negatively birefringent. KOH extraction renders the setae negative to a test for protein and reverses the sign of birefringence of the cortical material of the shaft.

Notizen: The marine priapulid Priapulus caudatus has a voluminous body cavity filled with a blood-like fluid containing erythrocytes and leucocytes (amoebocytes). The hematocrit of animals weighing 0.5-14 gm was 2-10%. The erythrocytes contain a hemerythrin blood pigment. The structure of the coelomocytes was studied by light and electron microscopy. The erythrocytes are nucleated and contain marginal bands, vacuoles and occasionally crystals. The cytoplasm has few organelles. The leucocytes are amoeboid motile cells, the cytoplasm of which contains numerous organelles. The most conspicuous of these are oval particles, probably representing developmental stages of lysosomes. Most of these organelles contain tubules stretching from one pole to another. In the hind part of the animal, certain tissues, primarily the posterior warts contain large numbers of coelomocytes. The histological picture is complicated, showing some resemblance to the lymphoepithelial tissues of vertebrates.

Notizen: The dissected tooth bearing bones of 20 specimens of Amia calva (Pisces:Holostei) ranging from the third to tenth season have been examined radiographically and in alizarin red S stained and cleared specimens. Although forms of alternate (1:1) tooth series replacement (sensu Edmund, '60) were frequently observed, even in the youngest, immature specimens, many examples of irregular replacement were recorded. In several bones, the maxillae in particular, series with every third (2:1) or fourth (3:1) tooth replacing were seen and possible patterns of 2:2, were recorded. It is concluded that these data are not consistent with the Zahnreihen concept but support a morphogenic field concept of tooth development.

Notizen: The first description of vertebral development in a plethodontid salamander is presented. Eurycea bislineata has larvae that hatch at a rather early stage of development. Somites and the notochord appear early. Somitic differentiation is slight, and no distinct sclerotome can be found. As a result, there is no clear primary segmentation of the skeletogenous tissue. No evidence of a sclerocoele can be found. The amount of sclerotomal cells surrounding the notochord is very low, relative to other tetrapods. Yet discrete perichordal rings of cells do form, in nearly midsegmental positions, and these give rise to the intervertebral cartilages. Osteogenesis of the centra is initiated prior to hatching and is coincidental with ossification of the neural arch. There is no sign of a neurocentral suture. The centrum forms as a thin shell of bone directly from sclerotomal cells. The notochord is a prominent feature of the vertebral column throughout life, retaining its integrity until late in life when some disintegration occurs locally. The notochord is filled with cartilage midvertebrally in late larval stages, and some additional cartilage forms later in life. The intervertebral cartilage enlarges greatly in late larval life. An opisthocoelous joint forms in this cartilage, apparently as a result of differential changes in the cells of the perichordal ring rather than by an invasion of cells from an external source. The intervertebral cartilage is a dominant structural and highly important functional feature of the adult vertebra. In metamorphosed individuals it may become extensively mineralized, and it consists of many different structural kinds of cartilage.The cranio-vertebral joint seems to form in a single segment, contrary to the condition reported by some early investigators. It is complex, and consists of articulations between the odontoid process of the atlas and the occipital arch, as well as between the occipital condyles and atlantal cotyles. The notochord plays a dominant role in the early development of the odontoid, but then changes radically and is absent in the adult process.The anterior trunk region seems to be much more conservative than posterior parts of the column. The patterns of nerve routes and nature of development of the ribs and rib bearers differs greatly from conditions elsewhere in the column. The rib patterns are similar to presumed ancestral conditions. Rib development on the sacral and caudosacral vertebrae is in some ways more similar to that of the anterior vertebrae than of the central trunk vertebrae.Quantitative aspects of variation in the vertebrae of adult salamanders are presented. There is more regional variation and less site variation than would be expected from literature reports.Evolutionary aspects of the origin of the cranio-vertebral joint, transverse process and ribs, patterns of segmentation, and centrum development are considered in the light of the new information on Eurycea. There is no evidence that more than one vertebra is involved developmentally or evolutionarily in the cranio-vertebral joint. The most generalized condition of rib bearers in living salamanders is one in which the dorsal and ventral bearers are in cartilaginous continuity during development. There are many variations on this theme in living species. It is inappropriate to speak of a resegmentation of the sclerotome in Eurycca, even though the adult vertebra is a transsegmental structure, because there is no primary segmentation of the scanty sclerotome. The important feature found in vertebral development in all tetrapods is the perichordal tube and its subsequent differentiation. Questinos concerning precise homologies of the salamander vertebral centrum with those of other vertebrates cannot be answered by data from development sequences with currently used criteria of homology. On the other hand, it appears that all centra, regardless of subdivision, are homologous in all tetrapods.

Notizen: The Oberhautchen of scales from the dorsal, parietal, and ventral regions of Sceloporus occidentalis (Iguanidae), Gerrhonotus multicarinatus (Anguinidae), and Anniella pulchra (Anniellidae) were examined with a scanning electron microscope. At low magnification, all scales of S. occidentalis exhibit well-defined outlines of cells belonging to the Oberhautchen layer and the previously overlying clear layer. The dorsal and parietal cells of this species exhibit a minutely dentate Oberhautchen that forms tooth-like spinules 0.2 to 0.5 μ long and arranged in irregular rows. Minute pits 0.1 to 0.3 μ in diameter characterize the Oberhautchen of a ventral scale.Cell outlines are not evident on the scales of G. multicarinatus. The Oberhautchen of dorsal and parietal scales of this species is prominently laminated. Laminae are less prominent on scales of the lateral fold, and no intrinsic surface structure is evident on a ventral scale. In contrast, the fossorial anguinomorph Anniella pulchra exhibits Oberhautchen surfaces with practically no intrinsic microornamentation. However, what appear to be outlines of Oberhautchen cells are visible on the dorsal and ventral scales.These observations suggest that modifications of Oberhautchen microornamentation may have evolved to reduce friction with the substrate or other scales. The lack of pronounced microornamentation of the Oberhautchen on some body scales may indicate that a complex interdigitation between clear layer and Oberhautchen cells is not essential to the sloughing process.

Notizen: Stolonic growth has been compared among several genera of calyptoblastic (Campanularia flexuosa, C. calceolifera, Gonothyraea and Sertularia) and gymnoblastic (Pennaria, Bougainvillia, Eudendrium and Cordylophora) hydroids with respect to such features as the (1) complexity and uniformity of the tip movements, (2) constancy of growth cycle duration, (3) variability in growth among cycles, (4) growth rate, and (5) variability of retractions among cycles.The “growth cycle,” previously described in C. flexuosa, is the basis for elongation in all species observed. Its pattern is indistinguishable between the Campanularia species; however, at the generic level the tip movements show peculiarities which delineate each genus from all others. In addition, the movements in all calyptoblasts are uniform from cycle to cycle and comparatively simple, whereas those of the gymnoblasts are complicated by the variable appearance of one or more secondary forward thrusts between crests.A dichotomy is seen between the calyptoblasts and most gymnoblasts in other respects as well. Cycle time is very predictable and cycle-to-cycle variability in growth is relatively narrow in all calyptoblasts. However, in most gymnoblasts both features are much more loosely regulated: only Pennaria shows some degree of control to its timing mechanism, and only in Bougainvillia and Eudendrium does the uniformity of growth per cycle reach the calyptoblast level.On the premise that calyptoblasts are evolutionarily the more advanced group, simplicity and regularity of growth movements are concluded to be the evolved, and complexity and variability the primitive, conditions. On this basis the evolutionary relations among the four gymnoblasts, as deduced from their stolonic growth behavior alone, are consistent in many but not all respects with those interpreted from morphological considerations.

Notizen: In order to clarify the morphology of the circulatory system of amphioxus the blood vessels were investigated using modern techniques of light and electron microscopy.The pattern of circulation in amphioxus is forward ventrally and backwards dorsally. In addition, circulating corpuscles, usually associated with the blood of higher chordates, are absent.The circulatory system of amphioxus consists of well defined contractile vessels and vascular spaces or sinuses within a connective tissue matrix. The contractile vessels have a discontinuous endothelial lining resting on a basal lamina and are enclosed by a simple layer of contractile myoepithelial cells. Discontinuous endothelial linings occur throughout the vascular tree, including major and minor afferent and efferent vessels and blood sinuses. This is in contrast to higher animals where the endothelium forms a more or less continuous lining along the inner surface of the boundary layer.It is suggested that the endothelial cells of amphioxus, like the endothelial cells in capillaries of higher chordates, most likely play a role in the physiology of the circulatory system by removing residues of filtration from the basal lamina, thereby facilitating an exchange of materials to and from the surrounding tissues.

Notizen: The development of the polarity and bilateral asymmetry of the future adult zooid has been traced to their earliest morphological expression in the palleal bud of Botryllus. The account is based upon continued observation of living buds. The polarized antero-posterior and dorso-ventral axes are first expressed by the skewing of a symmetrical, hemispherical bud towards the anterior end of the parental bud. Identification of these axes is reinforced by the development of a loop-like blood circulation, the primary circulation, in the horizontal plane during the enlargement of the skewed hemisphere to form a stalked vesicle. Bilateral asymmetry is first expressed by the asymmetrical expansion of the vesicle stage. The right posterior corner of the vesicle expands further posteriorly and becomes more acute than the left posterior corner. This larger expansion persists throughout the development of the right atrial cavity, which finally expands across the mid-line to partially surround the gut. The bilateral asymmetry, expressed in the expanded vesicle, is reinforced by the development in sequence of a rounded gut rudiment and a pericardial rudiment in positions that would be expected from the asymmetry of the expanded vesicle. The first appearance of the gut rudiment occurs earlier than had been recognized previously. Conflicting accounts of the time and mode of formation of the pericardial rudiment have been clarified. The results of this study are discussed in the context of determination of bud territory, polarity and bilateral asymmetry.

Notizen: Four glands of the house sparrow, chicken and turkey were examined histologically and for their content of amylase. These were the external and intermediate mandibular glands, the maxillary gland and glandula anguli oris of the sparrow and the anterior and posterior mandibular, maxillary and anguli oris glands of the chicken and turkey. Amylase was determined by a starch substrate slide method and by biochemical assay. General morphology and mucopolysaccharide staining are described.All four glands of the sparrow demonstrated significant amylolytic activity by the assay. In the external mandibular and anguli oris glands this activity could be traced to mucous and seromucous cells of origin by means of the starch substrate slide procedure. None of the glands of the chicken or turkey displayed significant amylolytic activity.

Notizen: The distribution of monoamine (catecholamine and 5-hydroxytryptamine)-containing nerve cell bodies in the brain stem and hypothalmus of the frog (Rana temporaria) was investigated with the help of the histofluorescence technique of Falck and Hillarp ('62). At the level of the hypothalmus of this amphibian brain, catecholamine-containing nerve cell bodies are found mainly within three areas of the periventricular gray substance, namely the peroptic recess organ, the paraventricular organ and the lateral recess region. On the other hand, most of the 5-hydroxytryptamine (serotonin)-containing nerve cell bodies of the brain stem of Rana temporaria appear to be concentrated within the midbrain tegmentum. This huge mesencephalic nerve cell collection can be subdivided into medial and lateral groups. More caudally, at the level of the isthmic tegmentum, another group of 5-hydroxytryptamine-containing perikarya located close to the midline, within the so-called raphae region, is clearly outlined. The latter group of neurons extends caudally as far as the level of the medulla oblongata. In addition, a small group of catecholamine-containing nerve cell bodies is also found in the ventromedial portion of the rostral midbrain tegmentum, whereas a few other catecholamine type neurons are scattered throughout the lower brain stem of the frog and more especially near the ependymal wall of the fourth ventricle. As a whole, the 5-hydroxytryptamine-containing neuronal systems of the brain stem of Rana temporaria are much more elaborated than the catecholamine neuronal systems of the same structure.

Notizen: The guinea pig soleus muscle is a convenient model for the study of slow-twitch intermediate (STI) fiber ultrastructure because it is composed entirely of fibers of this class. Such fibers were compared with fast-twitch red (FTR) and fast-twitch white (FTW) fibers from the vastus lateralis muscle.FTW fibers are characterized by small, sparse mitochondria, a narrow Z line and, an extensive sarcoplasmic reticulum arranged primarily in longitudinal profiles at the A band and with numerous expansions at the I band. Abundant mitochondria with a dense matrix and subsarcolemmal and perinuclear aggregations are typical of FTR fibers. These fibers contain a plexus of sarcoplasmic reticulum at the A band and a less extensive network at the I band. The Z lines are wider (890 ± 74 Å) than those of FTW fibers (582 ± 62 Å). STI intermediate fibers are distinguished from other types by wide Z lines (1205 ± 58 Å), a faint M band, and a less extensive sarcoplasmic reticulum. Compared to FTR fibers, STI fiber mitochondria are usually smaller with less notable subsarcolemmal accumulations.FTW fibers have a more limited capillary supply, rarely contain lipid inclusions, and thus may be restricted to phasic activity. Extensive capillarity, mitochondrial and lipid context, and fast contraction times indicate possible phasic and tonic roles for FTR fibers. STI fibers, characterized by numerous lipid inclusions, extensive capillarity, relatively numerous mitochondria, but slow contraction-relaxation cycles, are morphologically suited for tonic muscle activity.

Notizen: The haemocytes of Calpodes ethlius are described with the light and electron microscopes. Five fine structurally distinct types are distinguishable. However only three of these, the granular haemocytes, sphaerule cells and oenocytoids can be positively identified using a series of histochemical stains on smears and on thick sections of araldite-embedded material. The classification is based entirely on the structural features even though several suggestions concerning their function can be made from their fine structure. Intermediates having features of more than one cell type suggest developmental relationships.

Notizen: Four hemocyte types have been identified in the late last larval instar of Galleria mellonella. Plasmatocytoids are round to spindle shaped cells, 10-20 μ long and 5-10 μ wide. The cytoplasm contains no distinguishing inclusions. Golgi complexes, rough endoplasmic reticulum and free ribosomes are abundant. Granular hemocytes are oval shaped cells, 10-20 μ long and 5-10 μ wide. The granules, their most characteristic feature, have a diameter of 0.2 μ, a microtubular sub-structure, and are made up of acidic mucosubstances. Lipid droplets may be present in these cells at some stage of development. These cells appear to be phagocytic. Spherule cells are oval shaped, 15-20 μ long and 5-10 μ wide. The spherules, approximately 2 μ in diameter, have a highly ordered substructure and are made up of acidic mucosubstances. Oenocytoids are the largest cells, 20 by 40 μ. The cytoplasm contains mostly free ribosomes and microtubules.

Notizen: The epineurium of the esophageal complex of the gastropod pulmonate Triodopsis divesta was examined by electron microscopy. The epineurium consists of two main regions: an inner dense fibrous region adjacent to the avascular neural tissue of the ganglion and an outer cellular region comprised of a variety of cell types embedded in a connective tissue matrix. The dense fibrous region contains smooth muscle cells and associated nerve processes and is invested on the neural side by thin processes of glial cells. The outer highly cellular region contains smooth muscle cells, nerve processes, wandering cells (amebocytes), globular cells, and myoepithelial cells comprising the walls of the vascular system. In addition, a cell type not previously identified in other gastropod epineuria is present. These cells resemble neurosecretory cells. The morphology and structural interrelationships of these various constituents are presented and the possible functions of individual cell types and the epineurium in general are discussed in relation to information available on other molluscs.

Notizen: The muscles of the head, neck and thorax of the adult cabbage looper Trichoplusia ni are described for the first time. They are compared to those of Choristoneura fumiferana, Manduca sexta, Smerinthus geminatus, Antheraea polyphemus, Sphinx convolvuli, Crymodes devastator, and Danaus plexippus.

Notizen: A precise sequence of four morphological stages of head regeneration in the planarian Dugesia tigrina has been determined by light and electron microscopy. Each stage is identified by a particular morphogenetic process: I, wound healing; II, blastema development; III, growth; IV, differentiation. A wound epidermis consisting of a thin, sheet-like layer of cells, rapidly forms from undamaged epidermal cells at the wound margin. The early blastema is comprised of neoblasts which mature into regeneration cells. The maturational changes include the appearance of a nucleolus, nuclear pores, and perinuclear dense aggregates of granulofibrillar material in these cells. These elements are not evident in the neoblasts of the younger blastema. No mitotic cells are encountered in the blastema or wound epidermis. Cytoplasmic expansion of the regeneration cells is correlated with the formation of numerous microtubules radiating from a juxtanuclear centrosphere. During differentiation of muscle cells, distended, granule-studded cisternae, having moderately fibrillar contents, are regularly disposed adjacent to small patches of myofilaments. Presumptive epidermal cells are recognized by prominent “islands” of finely fibrillar cytoplasm. These cytoplasmic zones persist for a time during definitive differentiation when Golgi bodies, vacuoles, mucous droplets, and rhabdites become evident. The newly formed epidermal cells become inserted among the cells of the wound epidermis. Thus, cells of both the blastema and of the wound epidermis contribute to the reconstituted epidermis.

Notizen: Five different kinds of sense organs have been identified on the antennal flagellum of males of Ptilocerembia sp: (1) tactile hairs, (2) thick-walled chemoreceptors, (3) chemoreceptors with thick walls and many pores, (4) thin-walled chemoreceptors and (5) campaniform sense organs. The third type has not been reported previously for other species of insects and combines the characteristics of typical thick-walled and thin-walled chemoreceptors. The campaniform sense organs are situated in sets of three, 120° apart, on the periphery of the distal end of nearly every subsegment. They lie at the transition zone where the thicker cuticle of the subsegment changes to the thin membrane between subsegments.

Notizen: The rejection of skin homografts in the snake, Thamnophis sirtalis is preceded by an infiltration of mononuclear cells into the graft bed. The initial arrangement of infiltrating cells in perivascular halos suggests that these cells emigrate from the blood stream of the host. A cytological study showed that the vast majority of the cells can be classified as small and mediumsized lymphocytes, monocytes and macrophages. Early stages of infiltration were associated with large proportions of lymphocytes while later stages were characterized by a predominance of macrophages. It was concluded that the mononuclear cells associated with graft rejection include large proportions of lymphocytes and macrophages and not just one kind of lymphoid cell.

Notizen: Development of villi in the duodenum of the chick was studied in stages ranging from 11 days of incubation to one week after hatching. Formation of definitive villi is preceded by development of a set of previllous ridges that run lengthwise along the duodenum. The first set of 16 previllous ridges (Set I) is complete by about 13 days of incubation; all ridges in the set are fairly uniform and proceed through their subsequent development in synchrony. Previllous ridges in Set I fold into a highly regular zigzag pattern between 14 and 16 days of incubation. Definitive villi develop from Set I ridges beginning at about 17 days when populations of distinct cells appear on the crests of the ridges between angles in the zigzag folds. Cells in these populations lack the rounded appearance of cells seen in earlier stages; their apical surfaces are densely covered with microvilli. A second set of villi (Set II) develops at about 16 days of incubation when about 16 rows of tongue-like flaps erupt between the previllous ridges of Set I. At hatching, Set II villi are still smaller than villi of Set I; this distinction disappears by about the fourth day after hatching. The significance of the morphological changes in epithelial cells is discussed in terms of several hypotheses bearing on the mechanisms of villus formation.

Notizen: The fine structure of the ovary in the serpulid Spirorbis borealis has been described. The ovarian wall consists of from one to several layers of peritoneal cells. Peritoneal cell processes extend deep into the ovary and may be seen between developing oocytes. Although young oocytes may also be in close apposition to one another, intercellular bridges have not been observed. When primary oocytes at the surface of the ovary reach a diameter of about 20 μ, they start to erupt into the coelom. Ovulation results from a simple separation of overlying peritoneal cells which lack specialized cell-to-cell contacts. Once a free surface of an ovulating oocyte is exposed to the coelom, microvilli and primary coat develop. Previtellogenic coelomic oocytes are often observed in close proximity to putative neoblasts (perivasal cells), which suggests a possible functional relationship. The confusion that extists between germ cells, peritoneal cells, and so-called neoblasts in polychaetes is discussed.

Notizen: The ultrastructure of the centriolar satellite complex in the spermatozoon of the hydroid, Pennaria, is presented. The complex consists of nine spoke-like arms which emanate from the distal centriole and of nine wedgeshaped connectives which extend into the flagellum joining each of the alpha doublets and the flagellar plasmalemma. Based upon these observations a new model for the structure of the centriolar satellite complex is proposed. In addition, similar centriolar satellite complexes are reported in the spermatozoa of two echinoderms, Ctenodiscus crispatus and Thyone briareus, in support of the proposed model.

Notizen: Males of the European elm scale, Gossyparia spuria (Erioccoccidae) have two Malphigian tubules, each made up of mononucleate and binucleate cells. Both types of cells may contain heterochromatic (H) chromosomes which form an H body. The cells with H bodies (H cells) usually appeared singly anywhere along the tubule. However, when two or more H cells were present they tended to be closer to each other than would be expected by chance. The possible origin of this tendency is discussed. Following squashing, the nuclei of the binucleate cells were much larger than those of most other somatic cells, suggesting that they were highly endopolyploid. However, the H bodies of the cells of the tubules were of about the same size as those of the other cells. These observations suggested that the H chromosomes of the binucleate cells did not replicate while the euchromatic chromosomes of these cells replicated several times. The great majority of the nuclei of the H cells contained a single H body per nucleus. An analysis of the number of H bodies in binucleate cells indicated that when two H bodies were present in the same nucleus they usually did not fuse. Thus, they were believed also not to fuse in the mononucleate cells. Since almost all the mononucleate H cells had only a single H body (rather than 2) it was concluded that they did not originate from binucleate cells by nuclear fusion.

Notizen: The relation between muscle action and the mechanical properties of motor units has been explored in the main digit flexors of the cat hind limb: plantaris (PL); flexor digitorum brevis (FDB); flexor hallucis longus (FHL); and, flexor digitorum longus (FDL). General observations on muscle action revealed that PL is an ankle extensor as well as a digit flexor. PL and FHL were shown to be the major force contributors to digit flexion with FDL playing a lesser but still significant role.The mechanical properties of PL, FHL and FDB motor units were studied by noting twitch and tetanic tensions produced by electrical stimulation of single alpha axons, functionally isolated from the ventral root filaments. These data were compared to similar data reported by Olson and Swett (1966) for flexor digitorum longus (FDL). Our sample (114 PL, 60 FDB and 124 FHL units) disclosed that PL, FDB and FHL have units of uniformly fast contraction times (means 22, 27 and 27 msec respectively). PL units developed the most tetanic tension (3 to 160, mean 62 gm-wt) followed by FHL (2 to 87, mean 31 gm-wt) with FDB units producing very little tension (1 to 20, mean 6 gm-wt). Swett and Olson's FDL sample (108 units) showed tensions ranging from 0.3 to 100 gm-wt (mean 10 gm-wt).A division of labor among the four muscles is proposed. The large PL units are advantageous for forceful phasic inputs to the digits during the locomotion and in keeping with PL's additional role as an ankle exstensor. The low output forces of FDB units are optimal for discrete input to the digits during subtle adjustments of posture. We propose that the larger fast contracting units of FHL are used primarily for forceful digit flexions required in locomotion and for phasic protrusion of the claws while the predominately small and slow contracting units of FDL are used for sustained claw protrusion.

Notizen: The trabeculae cranii are at first quite separate from each other, after few days their anterior two fifths are connected by a trabecular plate which is obliterated throughout development. The paired origin of the parachordal plate is not observed. The fused posterior orbital cartilages chondrify in the form of a wide short plate, traversed by the oculomotor and trochlear nerves. The basicranial fenestra and fenestra ovalis are formed by the degeneration of pre-existing cartilage. The cochlear portion is completely fused with the parachordal plate from the very beginning. The elements of the pterygoquadrate are fused together. The quadrate and Meckel's cartilage are in close contact from the very beginning. While the lower part of the interorbital septum is derived from the trabecula communis, its upper part is derived from the anterior orbital cartilages. The lateral parts of the fused posterior orbital cartilages give rise to most of the taeniae and pilae of the orbitotemporal region. There is only one commissure between the auditory capsule and parachordal plate. A cartilaginous connection between the distal portion of the columella auris and ceratohyal persists for some time. The parietotectal and paranasal cartilages are fused together from the very beginning. The processus paroticus originates from the columella auris.In the fully formed stage the notochord is completely embedded in the occipital condyle. The union between the condyle and odontoid process persists. The auditory capsules and occipital arches contribute to the formation of the tectum synoticum plus posterius. The prefacial commissure and facial foramen lie in front of the cochlear portion. The columella auris possesses a processus internus (connected with the quadrate), but the processes a dorsalis has completely disappeared. The orbitotemporal region is quite complete. A medial fenestra is formed in the planum supraseptale. A fenestra is observed in each of the interorbital and nasal septa. The lamina transversalis anterior is fused with the parietotectal cartilage. A complete zona annularis is present. The outer wall of the paranasal cartilage is perforated by a large fenestra lateralis. The parietotectal and paranasal cartilages and the posterior process of the lamina transversalis anterior contribute to the formation of the concha nasalis. There is a contact between the planum antorbitale and nasal septum. The pterygoid process has disappeared. The common characters of the lacertid chondrocranuium are deduced.

Notizen: This investigation presents the ultrastructural changes that occur during previtellogenic and vitellogenic growth of the oocyte of a telotrophic ovary. The ovarioles of a newly emerged adult Rhodnius have their full complement of oocytes located at the base of the tropharium. These oocytes are in cytoplasmic continuity with the syncytial tropharium via trophic cords. The nuclei of these oocytes are in prophase of meiosis I with condensed chromosoes; synaptonemal complexes are visible in many. During oocyte growth the nucleus or germinal vesicle enlarges from a 3-4 μ diameter to a 45-50 μ diameter and the chromosomes become diffuse and arrested in late prophase I. Small previtellogenic oocytes are limited by a morphologically unspecialized oolemma and contain a pair of centrioles, rough endoplasmic reticulum, a few small Golgi complexes and clusters of mitochondria. By the end of previtellogenesis there has been an increase in the volume of the oocyte due to the transport of ribosomes and mitochondria into the oocyte from the tropharium. During vitellogenesis the oolemma develops a microvillous border and yolk precursors are internalized by pinocytosis. Small stacks of annulate lamellae, numerous ribosomes and the other organelles are restricted to the thin layer of cortical ooplasm; the lipid protein-carbohydrate yolk spheres and glycogen are located centrally. In oocytes not stimulated, autolysis occurs as dense local areas within the ooplasm.

Notizen: An electron microscopic study of several stages in the development of the glycogen body of the chick is reported. During early developmental stages (7.5-11 days) glycogen granules were scattered throughout the cytoplasm of glycogen-body cells. Lysosomes were observed for the first time on the eleventh day of incubation. In the course of subsequent development three well demarcated cytoplasmic areas became recognizable; a juxtanuclear region that contained most of the organelles and was devoid of glycogen, a peripheral area (ectoplasm) free of glycogen, and a region densely packed with glycogen. Cells that were heavily laden with glycogen contained unusual rounded or “C”-shaped multivesicular bodies which were associated with the Golgi complex and with Golgi-like vesicles. Their functional significance did not become evident in this descriptive study.The paucity of smooth endoplasmic reticulum indicated its lack of importance in glycogen metabolism in the glycogen body. Ribosomes, which were the only organelles consistently observed in close proximity to glycogen granules, were thus implicated in glycogen synthesis.

Notizen: A cytological and cytochemical survey was made of nucleolar changes during oocyte development in several different species of crickets (Gryllidae) representing the subfamilies Gryllinae and Nemobiinae. A large mass of extrachromosomal DNA is characteristic of the pachytene stage nuclei of all species examined. Nucleolar material accumulates at the periphery of the DNA body as the cells proceed into the diplotene stage of development. As the oocytes proceed through diplotene, the nucleoli reorganize into many small masses which eventually disperse in the nucleoplasm. These changes reflect both an increase in number and in size of the nucleolar material during the diplotene stage and the mode by which dispersal of nucleolar material is accomplished. These differences probably reflect differences in the organization of extrachromosomal nucleolar DNA.

Notizen: A histological evaluation of the effects of hypophysectomy and throxine therapy in young tail regenerates was carried out in the small iguanid lizard, Anolis c. carolinensis. Hypophysectomy caused a delay but did not inhibit blastema formation. The growth of the ependyma into the wound region was delayed in hypophysioprivic regenerates by about a week.Growth and differentiation of hypophysioprivic regenerates after blastema formation was variable, ranging from virtually no growth to the formation of a differentiated but very small protuberance. However, actual tail elongation was inhibited by hypophysectomy. In those hypophysioprivic regenerates that did show signs of differentiation, muscle groups were poorly defined, scanty in appearance and not as well differentiated as the cartilage tube.Thyroxine treatment in the young hypophysioprivic regenerates stimulated normal growth and normal appearance and differentiation of promuscle and procartilage aggregates as well as the growth of the ependymal tube into the blastema.

Notizen: Myocardial cells obtained from embryonic chick ventricles have been used to investigate (1) whether differentiated cells can undergo DNA synthesis and mitosis and, (2) whether heart cells when grown in culture can fuse with each other and with chick skeletal myoblasts to form heterokaryon myotubes. Electron microscopic observations have shown that myocardial cells of day 3 and day 20 chick embryos did contain myofibrils with defined sarcomeres; these cells have been observed in mitosis. Cells obtained by tryptic digestion of day 12 chick ventricles when grown in culture continued to replicate their DNA as shown by thymidine-3H radioautography with DNase controls and were observed in all stages of mitosis. Electron microscopy showed that myofibrils were present in some of the cultured cells.Bi-, tri- and tetranucleate cells were observed in the cultures. Thymidine-3H radioautography showed that these cells were formed by karyokinesis without cytokinesis and by the fusion of uninucleate cells. Since the heart cells could fuse with each other, we tested the possibility that they could fuse with skeletal myoblasts to form heterokaryon myotubes. This was accomplished by co-culturing thymidine-3H labeled ventricular cells and unlabeled skeletal myoblasts. Radioautography with DNase controls showed that some of the myotubes consisted of unlabeled skeletal muscle nuclei and labeled heart nuclei in varied proportions. The factors initiating the formation of these heterokaryons have not been elucidated.

Notizen: Morphological changes in the interstitial cells were studied during their differentiation into spermatozoa. Development of the spermatogonium involves an increase in nuclear and nucleolar size, and the formation of a dense mass of cytoplasmic ribosomes. The mature spermatozoon has a relatively simple structure. The head consists of a bullet shaped, homogeneous nucleus, which lacks an acrosome but bears distal membrane specializations. The middle piece is composed of four large spherical mitochondria at the base of nucleus. A single flagellum projects from one of the two centrioles lodged between the mitochondria. The flagellum appears early during development in the primary spermatocyte. During spermiogenesis microtubules associated with the basal body flagellum complex appear to define the axis of chromatin condensation.

Notizen: Both typical (haploid) and atypical (anucleated) spermatozoa reach the receptaculum seminis of inseminated females of Bombyx mori intermingled. However, only typical spermatozoa both leave the receptaculum and fertilize the eggs. Atypical spermatozoa, which are in fact anucleated flagellar apparatuses, probably function in transporting typical fertilizing spermatozoa to the receptaculum seminis. In the male ejaculatory duct both kinds of spermatozoa are wrapped with extra-cellular sleeves that presumably protect them on their way to the receptaculum. Typical spermatozoa “hatch” from the sleeves before leaving the receptaculum to fertilize the eggs. The presence of a centriole in the extra-testicular spermatozoa of this species supports the generalization that insect spermatozoa do have a centriole at the base of the flagellum.