ALBERT

Notizen: Summary Glial cells are present throughout the cerebral ganglia ofHelix pomatia, including the nerves, connectives and the commissure. Five types of glial cells can be distinguished on the basis of ultrastructural and organizational features. The topographic distribution of the various types is constant. Two main categories are recognized: 1. Filamentous glial cells (satellite cells of pericarya and axons): The long, thin and ramifying processes of these glial cells surround the pericarya or the axons and form the trophospongia. The ultrastructure and the spatial form of the trophospongia is described in detail. The main criteria of both glial cell types are the lack of organellar specialization, a high content of filaments and glycogen and numerous lipid droplets. A strong linear correlation exists between the index (relative number of glial cells per neuron) of the satellite cells of pericarya and the diameter of neurons in all ganglia, as shown by morphometric methods at the light-microscopical level. A mechanical supportive role and, more importantly, a metabolic function of these glial cells in relation to the neurons and axons is discussed. 2. Plasmatic glial cells (peripheral glia of the ganglia and the nerves, glia of the procerebral neuropile): These three glial cell types are characterized by a rather low content of filaments, particularly in the cell body, and above all by numerous dictyosomes and cytosomes, which indicates a high endocytotic activity. The plasmatic glial cells can be found throughout the periphery of the cerebral ganglia, except for the cortex of the procerebrum.

Notizen: Summary The ultrastructure of monociliary receptors in 10 species of the Proseriata and Neorhabdocoela is described, with particular reference to the epidermal dendritic part. Sensory cells with a single kinocilium situated at the level of the distal epidermis membrane are considered as mechano- or chemoreceptors. There exist sensory cells with a dendrite penetrating one epidermis cell and bearing an embedded kinocilium and a collar of 8 stereocilia or ridges with a fribrillose substructure. These collared receptors probably function as mechanoreceptors. In comparison with collared sensory cells in species of other turbellarian orders, the embedded receptors in the Proseriata and Neorhabdocoela are more advanced and possess synapomorphous characteristics. With the embedded receptors a new evidence is given for the close phylogenetic relationship between the Proseriata and Neorhabdocoela. The distribution of collared cells in the animal system and their phylogenetic implication for a choanoflagellate origin of the Metazoa are briefly discussed.

Notizen: Summary The rectal papillae ofThrips consist of four types of cells arranged as a closed hollow pad. The inner layer is composed of five large primary cells (“Hauptzellen”) and of a drain cell (“Kanalzelle”). The primary cells contain glycogen in form ofβ-granula, and multivesicular bodies. Their apical cell membrane, forming numerous leaflets is associated with mitochondria and with a coat of repeating subunits on the cytoplasmic surface. The lateral plasma membrane of the primary cells has a sinuous course and is in close contact with numerous mitochondria. The intercellular spaces of the primary cell complex are drained to the central cavity of the papilla by a discharge formed by a curved elephant's trunk-like process of the drain cell. The outer layer of the papilla consists of an inner and an outer secondary cell (“Nebenzellen”). Their differentiations related to fluid transport are evident, but generally less elaborate. An open communication of the lumen of the papilla with the haemocoel was not detected. The papilla is connected with the rest of the rectal epithelium by junctional cells (“Verbindungszellen”). Neurosecretory terminals are present at the base of the papillae. The possible ways of fluid transport are discussed and the structure of theThrips papilla is compared with that in other insects.

Notizen: Summary The scincid lizardTiliqua rugosa possesses a large external nasal gland which is located intraconchally. Highly ramified tubules, imbedded primarily in the periphery of the gland, unite to form collecting ducts which empty into a short excretory canal. The diameter of the tubules increases progressively from 30Μ. at the distal extremity of the gland to over 200Μ at the level of the collecting ducts. The intraglandular portion of the excretory canal is often dilated to form an ampulla. The thickness of the epithelium increases from 12Μ at the level of the tubules to 25–30Μ in the excretory canal. The excretory canal is lined with an epidermal epithelium close to the point where it enters the vestibule. In all the rest of the gland the tubules are lined with two cell types: large, typical muco-serous cells and “striated” cells. At the distal end of the tubules the “striated” cells are narrow and poorly differentiated and alternate more-or-less regularly with the muco-serous cells. The relative proportion of these “striated” cells increases progressively, as does their size, as one moves proximally down the tubule. In the gland as a whole the “striated” cells are approximately twice as numerous as the muco-serous cells but, due to their smaller size, they occupy less than one third of the tubular volume. Electron microscopy of the “striated” cells ofTiliqua rugosa revealed the presence of extensive lateral interdigitations and expansions of the basal cytoplasmic membrane, anatomical specialisations which are normally indicative of active salt transport. These modifications are less marked however than in the external nasal glands of the lizardsLacerta muralis andVaranus griseus, which do not appear to function as salt glands. In addition there are few mitochondria present, although they are of large size. The combination of these ultrastructural features, plus the fact that the “striated” cells are intermixed with muco-serous cells in the tubules, makes it most unlikely that the external nasal gland ofTiliqua rugosa is capable of elaborating an hyperosmotic fluid. What is more, this has never been conclusively demonstrated in this species in physiological studies. The progressive specialisation of the “striated” cells from the distal to the proximal section of the tubules poses the problem of the origin and differentiation of this cell type. A review of results obtained from the study ofTiliqua rugosa and other species of lizards shows that the nature of the relationship between structure and function of the external nasal gland is far from clear. The existence of “salt glands”, capable of excreting hyperosmotic solutions, is invariably linked with the presence in the gland of well-developed “striated segments” composed almost entirely of cells possessing extensive interdigitations of the lateral membranes. Amongst terrestrial lizards, nasal salt glands are usually found in herbivorous species and they are primarily adapted to the extrarenal excretion of potassium ions. The problem for carnivorous species is more often that of an excess of sodium rather than potassium ions and with the possible exceptionAcanthodactylus species, functional nasal salt glands have not been demonstrated in terrestrial carnivores, despite the presence in some cases of well-developed “striated segments” in the gland having a similar structure to those found in herbivores. In humid regions, carnivorous lizards probably never require extrarenal excretory mechanism and in arid regions their survival is assured by their capacity to tolerate hypernatraemia when confronted with excessive salt loads. Salt glands capable of eliminating sodium ions to any extent have only been described in two littoral species, an herbivorous iguanid and a carnivorous varanid. Unfortunately the structure of their respective nasal glands has not yet been described and their further study would be desirable.

Notizen: Summary The embryo ofOncopeltus fasciatus forms a typical secondary dorsal organ (SDO). It develops after katatrepsis from the contracting serosa, the cells of which decrease in diameter but increase considerably in height. After 66 h, the SDO represents a protrusion of the serosal epithelium above the head and is then reduced to a disc-shaped formation, which sinks into the yolk, where it disintegrates after 80 h. During its typical expression, between 66 and 78 h, the SDO shows a zonal arrangement of its cell organelles. The nucleus, which is located in the basal cell region, has a very irregular outline and includes several nucleoli and globular inclusion bodies. Rough and smooth ER are well developed around the nucleus and suggest the involvement of the organ in protein secretion as well as in lipid metabolism. Electron-lucent vacuoles and electron-dense granules, sometimes enclosed in the vacuoles, accumulate in the apical cell region, and are obviously extruded into the peripheral (extraembryonic) space. The formation of intercellular clefts and delicate cytoplasmic extensions facing the yolk and microvilli facing the periphery evidence a transporting function of the epithelium. Blisters intercalated in extended junctional complexes between apical cell regions point to the transport of solutes. Because of the similarities of the processes observed in the SDO and in Malpighian tubules of larvae, an excretory function of the SDO is suggested. Final products of yolk and embryo are apparently transported to the extraembryonic space, where they accumulate during embryogenesis. Phylogeny, relationship, and function of the different embryonic glands in Arthropoda (primary and secondary DO and pleuropodia) are discussed.

Notizen: Summary Biomphalaria (Australorbis) glabrata has a preradular as well as a postradular pocket and a collostyle hood. The odontophore cartilage does not consist of cartilage, but of cells which are characterized by numerous vesicles, mitochondria, and muscle fibres in the periphery; other cells contain large amounts of glycogen. The odontoblasts are characterized by unusually long microvilli which reach into the newly formed radula teeth. The formation of a tooth begins above the posterior odontoblast which has at first only short microvilli. The tooth seems to be raised by the extension of these microvilli. Microfibrils are formed in the electron dense material which is present in the small space between the microvilli; probably these microfibrils contain chitin. Obviously the interlacing of the bundles of microfibrils in a tooth corresponds with the complex arrangement of the long microvilli during formation of the tooth. Finally the microvilli are integrated into the newly formed tooth and radular membrane. Several odontoblasts join to form a single tooth. The radular membrane is secreted mainly or exclusively by the most anterior odontoblast. The cells of the superior epithelium surround the radula teeth. The so-called “secretion cavity” seems to be an artifact. Electron dense material is present between teeth and superior epithelium which is not apposed to but seems to be integrated into the teeth. The cells of the inferior epithelium show considerable secretory activity; the secretions seem to be incorporated into radular teeth and membrane.

Notizen: Summary The young recent cassiduloidEchinolampas depressa has a lantern and teeth which are fully developed, but which never function because they disappear completely after metamorphosis. The lantern resembles morphologically that of the clypeastroid family Fibulariidae. The teeth are built-up of tooth elements, which have small primary plates, large lateral plates, and a cluster of prisms, and they are nearly identical to the teeth of fibulariids. In addition, the fine structure of teeth from liassic fossils was analyzed. This was the first investigation ever of the microstructure of fossil echinoid teeth. The examined teeth were well preserved, and proved to have nearly the same structure as the teeth ofEchinolampas. The results of this investigation prove that teeth of cassiduloid-clypeastroid structure were already in existence in the Liassic. Using micro structure as a comparative basis the author distinguishes between echinoid teeth of the “clypeastroid type” (present in Cassiduloida, Clypeastroida, and in all probability in Oligopygoida), and those of the “regular type” (present in all recent regular echinoids and in all probability in Holectypoida). The well-known aulodont, stirodont, etc., types of teeth and lanterns belong to the regular type. Teeth of the regular type are highly complex in structure, and certainly cannot be the result of evolutionary convergence. From the morphological point of view the clypeastroid type is the simpler one, and there is no indication that it is the result of secondary simplification. For this reason the anatomical features of the clypeastroid type of echinoid teeth are considered to be the more primitive. Contrary to the opinion of several authors, this author maintains that echinoids possessing a masticatory apparatus of the clypeastroid type are by no means descendents of stirodont ancestors.

Notizen: Summary Numerous short ciliary structures are described in immature spermatozoa of a marine catenulid,Retronectes atypica (Doe and Rieger, 1977). These ciliary structures are associated with spherical bodies consisting of concentric flat vesicles. Since such spherical bodies have been described for several other species of Retronectidae (Sterrer and Rieger, 1974), it is assumed that the multiple ciliary structures may be a characteristic of the whole family. Nuclear morphology and other cytological structures are described for mature and immature stages of spermatogenesis. The finding of these ciliary structures is thought to underline the unique and isolated position of the Catenulida within the Platyhelminthes and the lower worms as a whole.

Notizen: Summary The ocellus of a synaptid holothurian,Opheodesoma spectabilis, is composed of sensory and supportive cells and underlain by numerous bundles of tentacular nerve fibers. Pigment cells in the tentacular nerve envelope the ocellus. A sensory cell is divided into three parts: an apical part from which a single cilicum and numerous microvilli arise, a slender middle part, and an enlarged basal part that contains an oval nucleus and gives rise to an axon. The axonemes in the cilia show varying degrees of remodelling. The following changes result from exposure to light: the microvilli become shorter and irregularly arranged; plasmalemmal invaginations engulf the microvilli; coated vesicles of varying appearances and membranous fragments become abundant; microtubules are less evident in the apical part; and small flat vesicles appear along the plasma membrane in the middle part. The evolution of photosensory cells and membrane turnover are discussed.

Notizen: Summary 1. Studying speciation processes ofGyratrix hermaphroditus 16 populations from 15 little ponds in Lower Saxonia were examined. 2. Basically two types of life-cycles are recognized in populations ofGyratrix. Polyvoltine cycles from April to October and sometimes over the winter months occurred in eurytherm populations. Dormance periods are facultative. The life-cycles of the psychrophileous populations are univoltine from February or March to May or June. A period of 9 months or more is survived in the egg capsules by a diapause. 3. In morphology the form and largeness of the egg capsules and the male cuticular-organs is significant different in small, medium-size and large specimens. The chromosome-set of a medium-size population is tetraploid with 2n=8,n=4. Numbers of chromosomes of all other populations are 2n=4,n=1. 4. Reproductive isolation exists between five populations. ThereforeGyratrix is considered as a group of closely related species forming at least five sibling species. The range of two populations is unknown. The biota of the sibling species are isolated ponds or ponds in the neighbourhood one to another. In one case two species are living sympatric in the same pond. 5. The origin of the speciation processes are refered to autopolyploidy, ecogeographical differenciation and change of chromosome structure. Primarily the reproductive isolation is caused by a sexual substance, inhibiting copulation. It is different in all populations. 6. The supposition pointing out further sibling species from marine, brackish and limnetic biota renounced us to give a taxonomic term. The species groupGyratrix hermaphroditus is provisionally carried on under this name.