NIDAMENTAL TISSUES 



485 



form an almost solid mass with but little connective tissue between them, 

 and the gland-cell nuclei lie flat in the cells. On the other hand, the 

 distal parts do not lie so 

 close to one another, but 

 are separated by a consid- 

 erable space filled with the 

 typical molluscan connec- 

 tive tissue with its coarse 

 reticulum and many alveoli. 

 In the figure it can be seen 

 that blood channels occur 

 in these spaces. The se- 

 creting cytoplasm of the 

 gland cells shows a deli- 

 cate reticulum with fine, 

 black granules at the inter- 

 sections of its strands, and 

 large, light-blue staining 

 granules in the meshes. 

 These latter are probably 

 the secretion; the first are 

 possibly microsomes. 



The opening of these 

 glands is exceedingly small 

 and hard to see, among 

 the epithelial cells on the 

 primary surface. Figure 

 455 shows the single distal 

 part and double fundus of 

 one of these glands as indi- 

 cated by the dotted lines 

 on Figure 454. The cells 

 lining the surface outside 

 of the groove show no mucin inclusions, and have very large basal 

 granules on the marginal ends of their short, strong cilia. These 

 cilia are used to move the eggs and egg cases, there being no peri- 

 stalsis. 



Among the vertebrate animals we shall examine the histological struc- 

 ture of the nidamental organs of: first, a urodele amphibian that forms 

 two jelly coverings for its individual ova; second, a teleostfish that forms 

 a single jelly covering for a great many of its eggs; third, a selachian fish 

 that forms an albumen covering followed by a tough, chitinous covering 

 for each of its eggs; and, lastly, a bird which forms a tough albuminous 



FIG. 455. Distal and proximal extremities of a com- 

 pound tubular nidamental gland from the oviduct of 

 Sycotypus canaliculatus . The actual opening of the 

 duct is small and obscure, and its location is indicated 

 in the figure by the depression in the ciliated epithe- 

 lium. X 500. 



