EMBRYOLOGY OF CRYPTOBRANCHUS 81 



tions as the innermost lamella of the capsule. The entire inner 

 layer of the capsule of Necturus has a tough consistency similar 

 to that of the vitelline membrane of Cryptobranchus ; this per- 

 haps is the reason why it is so slow in enlarging. 



In Necturus the egg proper is slightly smaller than that of 

 Cryptobranchus; in the early cleavage stages it measures about 

 5.8 mm. in diameter. 



A general description of the gelatinous envelopes of several 

 species of Amblystoma has been given in a previous paper (Smith 

 '11). 



5. The sperm 



The spermatozoon- (fig. 3) has been figured by Reese ('04), 

 who fails, however, to picture the middle-piece. The sperma- 

 tozoon is about 225/i long, and stout in structure as compared 

 with the spermatozoa of Amblystoma and Diemyctylus. The 

 head, excepting the acrosome, stains deeply with Delafield's 

 haematoxylin. The acrosome appears to be uniformly tapering, 

 not spear-shaped as in Amphiuma (described by McGregor, 

 '99). As stated by McGregor ('99) the middle-piece in Crypto- 

 branchus is very short in comparison with that of other urodeles. 

 The tail-piece is provided with an undulating membrane, bordered 

 with a convoluted filament. 



The ripe spermatozoon is motile, as regards both shaft and 

 filament ; but the spermatozoon as a whole is not so flexible as the 

 more slender spermatozoa of Amblystoma and Diemyctylus. 

 This greater rigidity of the spermatozoon is perhaps correlated 

 with the method of fertilization: the spermatozoon must pene- 

 trate the tough and thick egg capsule after a brief exposure of the 

 latter to the hardening effects of water. 



In seminal fluid obtained from occasional individuals, an oval 

 mass of granular protoplasm, about IS/x by 16/^, surrounds the 

 posterior part of the head of the spermatozoon. The long axis 

 of this bead-like mass coincides with that of the spermatozoon. 

 I have found a similar mass of protoplasm present in spermatozoa 

 from some individuals of Amblystoma punctatum, but here the 

 oval mass usually occurs about the junction of the head and mid- 



