EMBRYOLOGY OF CRYPTOBRANCHU5 ALLEGHENIENSIS. 149 



These figures represent the average of several measurements, 

 the range of variation of the first dimension being small, of the 

 others considerable, in eggs from the same parent. The egg 

 proper ordinarily sinks to the bottom of the fluid which sur- 

 rounds it, so that when viewed from above it is magnified by the 

 lens-shaped capsule so as to appear considerably larger than is 

 indicated by direct measurement. 



Occasional strings of egg capsules are found without any eggs 

 enclosed. These empty egg envelopes have the same structure 

 as the others, and usually occur as a portion of a string of cap- 

 sules the remainder of which contains eggs. A few of the empty 

 egg capsules are double, formed by the union of two capsules 

 without a connecting cord ; in such cases the cavities of the 

 two capsules are separated only by a very thin gelatinous 

 septum. 



In fertilized eggs in an early stage of development, preserved 

 in formalin without removal from their envelopes, I found float- 

 ing in the liquid between the egg and its envelope a fairly large 

 irregular and slightly opaque mass, in appearance like a faint white 

 cloud (see Fig. i). This mass had not been noticed in the cap- 

 sule of the living egg, probably because it was then transparent. 

 Under the microscope it was found to consist of a clear gelatin- 

 ous matrix in which were embedded numerous large round cells 

 each with a very large nucleus and often with what appeared to 

 be a large vacuole. By the use of a dissecting lens the individ- 

 ual cells could be seen while still within the envelope. In some 

 egg capsules they occur diffused throughout the liquid of the 

 cavity, not aggregated in a mass to form an opaque body. 

 Numerous spermatozoa are present in the opaque body, but they 

 also occur floating in the surrounding liquid and embedded in the 

 egg capsule. Whether the opaque body is present in unfertil- 

 ized eggs I have not at present the material to determine. The 

 unfertilized eggs of Cryptobranchus allegheniensis have been 

 briefly described by Reese ('04) but without mention of any such 

 feature as the opaque body described above. Both opaque body 

 and spermatozoa regularly occur in egg capsules that do not con- 

 tain eggs. The origin and function of the cells of the opaque 

 body are at present problematical. 



