NIDAMENTAL TISSUES 483 



are permanent cells and not destroyed in the process of forming the 

 secretion. 



The real cytoplasmic body of these gland cells is hard to define on 

 account of the large amount of secreted material with which the cells 

 are filled. The nucleus lies proximal in the cell and is large, and usually 

 round. Its plasmosome is larger than any other found in the tissues of 

 Lumbricus except in the young ova and in some nerve cells. Toward 

 the gland mouth and lining the exterior, the nuclei are somewhat smaller 

 and inclined to be oval. The distal part of the cell body is bent up and 

 extends up through the lumen toward the mouth of the gland. To- 

 gether with the same parts of its fellow-cells, it fills the lumen, and one 

 cannot determine easily where the cell ends distally. The secreted 

 material is very clear, and, if granular, is very finely so. In the peripheral 

 part of the gland the secretion is more coarsely granular. 



That part of the epithelium which touches the exterior is entirely 

 different in appearance. The cells are very narrow, and their nuclei 

 are also long, narrow ovals in shape. The nucleus has a more abundant 

 supply of chromatic material, and the plasmosome is smaller than the 

 nucleus of the deeper cells. These cells also secrete, but the material 

 is not so abundant. 



Very highly developed female nidamental tissues are to be found 

 among the mollusks. They are used to make both individual and col- 

 lective envelopes for the ova. One especially interesting one is to be seen 

 in the gasteropod, Sycotypus canaliculatus, in which the egg case is formed 

 in a heavy-walled, glandular part of the oviduct. The tough and mem- 

 branous walls of the many egg cases, as well as the string to which they 

 are regularly attached, are all secreted by the glands found in the walls 

 of the oviduct, a long tube which carries the eggs to the exterior. 

 The eggs come into the oviduct in groups of from 40 to 150, 

 in a medium-sized specimen. Each group lies in a fold in the thick, 

 glandular wall, and this fold forms a case around it. The glandular 

 thickness occupies two longitudinal bands of the lining of the duct, and 

 on one side, where they meet, is a long groove in which the string 

 that bears the cases is formed in situ with the cases attached to it. The 

 epithelium lining this groove is different from that which secretes the 

 materials for the cases. Figure 454 is a rough diagram of one side of the 

 groove, and a small portion of the glandular thickening on the same 

 side. 



At the bottom of the groove it is least differentiated and is a columnar 

 epithelium with rather narrow cells and nuclei. On the lower side of 

 the groove it begins to be thrown into folds and an occasional large "gob- 

 let cell" full of mucin granules is seen, especially on the top of the folds. 

 This condition is exaggerated nearer the top of the groove, where the 



