Comparative study of the choanosome of porifera: II. The keratose sponges.

The aquiferous system of representatives of the orders Dictyocer-atida, Dendroceratida, and Verongida has been studied to note its relevance to the systematics of the groups. The volume of the choanocyte chamber, the size and shape of the choanocytes, the number of choanocytes per chamber, the relative development of the mesohyl, and the features of endopinacocytes are estimated from scanning and transmission electron microscopic observations of representatives of most families of the three orders. Although the Dysideidae have a reticulate skeleton and were classified in the order Dictyoceratida, they are actually closer to the Aplysillidae (Dendroceratida) than to dictyoceratids.

Comparative study of the choanosome of Porifera: 1. The Homoscleromorpha.

The choanoderm and pinacoderm of representatives of the two families of Homoscleromorpha sponges, the Oscarellidae and Plakinidae, have been examined by transmission and scanning electron microscopy. Different fixative procedures have shown the dramatic influence of fixation conditions on the morphology of choanocytes. These two families of sponges have the following morphological features in common: flagellated endopinacocytes with short apical microvilli and basal pseudopods; the presence of a very thin and dense sheet of matrix material which limits the mesohyl.

Immunohistochemical studies on the distribution and the function of the D-galactose-specific lectins in the sponge Axinella polypoides (Schmidt).

The distribution of the two D-galactose-specific lectins within the sponge tissue of Axinella polypoides was studied by autoradiography and by an immunohistochemical method on paraplast- and cryosections. Both techniques revealed that the lectins are stored inside the vesicles of the spherulous cells. All spherulous cells, regardless of their appearance in the different types of tissue contained the lectins.

[Ultrastructural aspects of sheep choroid plexus cells during exogenous cell fusion induced by Visna virus in vitro].

During the first moments of the in vitro infection of Sheep choroid plexus cells with high multiplicities of infection of Visna virus, the authors observed: a strong development of GERL, some signs of an intensive protein synthesis and numerous filament bundles. This infection leads to an exogenous cell fusion.