108 BERTRAM G. SMITH 



in the material. Since during this time, which inchides t'he win- 

 ter months, development is least active, the lack of these stages is 

 of minor importance for the purposes of the present paper. 



1 . The formation of the follicle and the egg membranes 



The young ovary of Cryptobranchus is essentially a sac with 

 thick cellular walls. In a 9 cm. larva the ovarian wall (see figs. 

 13 to 17) shows structural differentiation as follows: (a) an inner 

 and an outer limiting membrane of flattened epithelium; these 

 membranes are connected by (6) a network of cells of a character 

 similar to those comprising the limiting membranes, though usually 

 not so greatly flattened; within the meshes of this network are 

 found (c) young ovocytes in various stages of development. 



In the ovary of a 9 cm. larva, more or less clearly defined 

 groups or cysts of very young ovocytes (see fig. 13) may be found, 

 each group surrounded by a thin epithelial membrane, the cyst 

 membrane. All the ovocytes of each group or cyst are presum- 

 ably the product of a single primary ovogonium. Epithelial cells 

 also occur within the cyst. Within many of these cysts, develop- 

 ment has gone further, and some or perhaps all the ovocytes have 

 undergone an increase in size which involves both nucleus and 

 cytoplasm (see fig. 14). Within each cyst, one ovocyte usually 

 outstrips its fellows, and becomes surrounded by a layer of epi- 

 thelial cells which form the follicle (fig. 15). 



With a further increase in size of the ovocyte, the follicular 

 layer assumes the character of a definite membrane with some- 

 what flattened cells, and that portion of the cyst membrane in 

 contact with the ovarian membrane shows an increase in the num- 

 ber of its nuclei and is more clearly differentiated as a separate 

 layer (see fig. 16). 



With a still greater increase in size, as shown by the most 

 advanced ovocytes of a 9 cm. larva and in later stages, the egg 

 presses the overlying membranes into the central cavity of the 

 ovary, so that the ovocyte comes to be suspended as in a sac, and 

 is more nearly surrounded by the cyst and ovarian membranes 

 (see figs. 17 to 21). In all three membranes, an increase in the 



