EMBRYOLOGY OF CRYPTOBRANCHUS 73 



that in Cryptobranchus the mechanical stimulus can hardly be 

 the true cause of the formation of the capsule, since capsules are 

 formed when only a small drop of coelomic fluid is present. More- 

 over it is here observed that coelomic fluid may pass down the 

 oviduct without becoming enclosed in such capsules; on the other 

 hand, every egg is provided with a capsule. 



When distended with eggs, the uterus is spindle-shaped, about 

 10 cm. long, with a transverse diameter of about 4 cm. at its wid- 

 est part. Its thin walls have a rich blood supply. 



Apparently the eggs do not, as a rule, remain long in the uterus 

 before spawning takes place. During the breeding season com- 

 paratively few females are found having eggs in the uteri; the 

 majority of the females captured are either spent or with eggs 

 still in place in the ovaries. Eggs taken from the uteri are, in the 

 great majority of cases, capable of artificial fertilization; this 

 subject will be more fully discussed later. 



(b). Oviposition, and nesting habits. Under strictly natural 

 conditions egg-laying takes place under cover of rocks in the bed 

 of the stream ; but in creek aquaria, arranged to afford conditions 

 as natural as possible without too much cover, the process has 

 been repeatedly observed. 



Egg-laying begins slowly, a short string of eggs sometimes 

 protruding from the cloaca for several hours before spawning 

 begins in earnest. In the natural habitat, such short strings of 

 eggs are often found in the open. Later, two long strings of eggs 

 proceed slowly from the cloaca, one from each uterus; the majority 

 of the eggs are then deposited more rapidly, in multiple strands, 

 the process requiring less than five minutes. When egg-lajdng 

 is completed, the strings are usually twisted together in a single 

 tangled mass. 



The 'nest' of Cryptobranchus allegheniensis has already been 

 described as either a burrow or a natural cavity under a rock 

 which is wholly or partially submerged. The eggs are not fas- 

 tened in any way, but are protected by this sheltered position 

 from being swept away by the current. 



The nests of Cryptobranchus japonicus have been described 

 by Ishikawa ('04), and closely resemble those of C. allegheniensis. 



