Regeneration der Tentakel und des Auges bei der Spitzschlammschnecke (Limnaea stagnalis L.)

Ohne Zusammenfassung     

Degradation of the radula in the snails Biomphalaria glabrata say and Limnaea stagnalis L. (Gastropoda,Pulmonata)

Summary The radula of snails is formed at the posterior end of the radular gland or pocket, and degraded at the same rate at its anterior end. Degradation is due to different secretory activities of the inferior epithelium of the radular gland. Its secretions seem to degrade enzymatically the matrix of the radular membrane and basal plates of teeth, leaving only chitin containing microfibres and degradation products. The sclerotized parts of the teeth remain unchanged, but as they are now only loosely connected with the radular membrane. they are torn off easily during feeding movements. The rest of the degraded and frayed radular membrane and the subradular membrane are also lost by abrasion during feeding. The cells of the inferior epithelium are connected with each other by septate desmosomes and an elaborate system of deep lateral interdigitation which may provide tensile strength. Extrusion of degraded cells of the inferior epithelium into the subradular membrane takes place, although the thick basal lamina forms a continuous sheath which is closely adjoined to the basal parts of the inferior epithelium. Nerve fibres containing vesicles with electron dense neurosecretory material (deduced from the diameter of 200–250 nm) are attached to this sheath or penetrate into it; they may be involved in the regulation of production and degradation processes during radula replacement. Problems of the forward transport of radula and inferior epithelium are discussed.     

A cytochemical study of oocyte growth in four species of millipedes

Summary The cytochemistry of oocyte growth was investigated in four species of millipedes; Narceus americanus, Oxidus gracilis, Cheiropus plancus, and a Pleuroloma species, probably P. cala. The oocyte of all four species produced a yolk nucleus which arose in contact with the nuclear membrane, subsequently detached, migrated into the central ooplasm and disrupted coincident with the appearance of protein yolk granules in the oocyte cytoplasm. Since the follicular epithelium did not display any morphological or cytochemical manifestations of secretory activity, it is suggested that direct incorporation of exogeneous proteins into yolk may play a lesser role in vitellogenesis in these forms than in insects and many other animal groups. Ooplasmic RNA levels achieved a maximum before vitellogenesis was initiated and then decreased. Similarly the nucleoli increased in size and RNA content up to the point at which cytoplasmic RNA levels began to decline. Basic proteins associated with RNA were present in the oocyte cytoplasm and the nucleoli. These achieved a peak concentration in the same size oocytes as RNA, but the intensity of staining decreased more rapidly than that of RNA during subsequent growth. The concentration of nucleoplasmic protein in oocytes of all four millipede species increased in the germinal vesicles during the course of oocyte growth. Coincident with the initiation of vitellogenesis, a class of cytoplasmic inclusions was developed which have been called concentric ring bodies. These inclusions consist of concentric layers of organic matrix material with crystallized calcium salts sandwiched between. These probably represent calcium reserves which are utilized in the formation of the exoskeleton by the embryo.Presented in partial fulfillment of the requirements for the Master of Science degree to the Graduate School of Arts and Sciences of the University of Florida.This work was supported by the following U.S. Public Health Service grants: Pathology Training Grant 5-T1-GM-1142-03, and to R. R. C. HD-1499-04 and Career Development Award K-3-HD-6176-04.     

Chemical sensitivity of Limnaea stagnalis neurons and their responses to synaptic stimulation

Responses of nerve cells to puncture, to touching the surface of the mollusk leg, osmotic stimulation, and extracellular microiontophoretic injection of acetylcholine, noradrenalin, serotonin, atropine, and propranolol were recorded intracellularly in the right parietal, left pedal, and visceral ganglia of the unisolated circumpharyngeal ring ofLimnaea stagnalis. Selective sensitivity of the neurons to the biologically active substances was observed. Results indicative of the functional differences between the various ganglia and of their neurochemical organization were obtained. Selective blocking of the unit responses to puncture of the surface of the mollusk leg by atropine or propranolol suggests that different forms of excitation reaching the central neurons evoked different and specific neurochemical processes on their subsynaptic membranes which can retain the essential informativeness of the widely different afferent volleys converging on a single nerve cell.I. M. Sechenov First Moscow Medical Institute. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 510–518, September–October, 1973.     

Dynamics of zona pellucida formation by the mouse oocyte. An autoradiographic study

The dynamics of the synthesis of the mouse oocyte zona pellucida was studied using light microscope autoradiography after intrabursal injection of (3H) -fucose. Zona accretion occurred continuously from the inside, demonstrating that the oocyte itself elaborated all the raw material of the zona. The duration of zona synthesis corresponded to that of the oocyte growth phase. Zona secretion stopped one week before ovulation and there was no renewal of its material.     

Replication bands and nucleoli in the macronucleus of Euplotes eurystomus: an ultrastructural and cytochemical study

The principal structural compartments of the macronucleus of Euplotes eurystomus were examined by ultrastructural and cytochemical procedures. Interphase chromatin is condensed in highly compact granules that stain intensely with the DNA-specific osmium-amine procedure. Nucleoli react strongly with silver and with thiol-specific reagents, but are almost completely unstained by osmium-amine. The organelle of DNA synthesis, the replication band, is composed of 2 zones. The forward zone consists of highly ordered chromatin fibers, stains strongly with osmium-amine, with silver, and with thiol-specific reagents. The rear zone, which is the site of DNA synthesis, is impoverished in DNA, and is very sensitive to collapse induced by in vivo heat shock, or during nuclear isolation.