A cytological study of the neurohypophysis of Scylliorhinus caniculus.

Abstract

1. In the pars nervosa of Scylliorhinus two types of pituicytes are described : relatively small irregular cells with thin branching cytoplasmic processes and large parenchymatous cells. 2. The parenchymatous pituicytes originate from the ependymal layer and possess secretory activity; their products are extruded into the spaces between the fibres of the pars nervosa. 3. A discussion is given concerning the identity of these cells with some special Herring-bodies, as described by Scharrer, and of the probability of the formation of neurosecretory material by these cells. 4. Ependymocrinie is described for the cells of the ependymal layer of the pars nervosa. 5. Migration of isolated intermediate cells was observed and also of parts of the pars intermedia into the pars nervosa. The penetrating tissue tends to make an extensive surface of contact with the fibrillar tissue of the pars nervosa. 6. In correlation with this migration of intermediate cells, the absence of ependymal structures above the region of penetration is established, and the possibility of hydrencephalocrinie is discussed. 7. It is concluded that the pars nervosa of Scylliorhinus is not merely the sum total of nerve endings and therefore an exception in the series of Vertebrates, but an organ that in its histological and cytological details is in accordance with the data described for the pars nervosa of other Vertebrates.