53(5 BERTRAM G. SMITH 



embryo shown in figure 200. The total hulk of this double em- 

 bryo is about equal to that of an ordinary single embryo from 

 the same spawning. That the occurence of such a monstrosity 

 in this species is exceedingly rare in nature is shown by the fact 

 that during the past seven years I have collected many thousands 

 of embryos from nests, yet in no other instance have I found an 

 abnormality even approaching the one under consideration. 



Fig. 200 Double ombryo of Cryptobranchus allegheniensis. Photographed 

 after preservation in formalin. X 4. 



The precise manner in which the double embryo originated 

 is problematical. Single capsules sometimes contain two eggs 

 in close contact; but the small size of the double embryo pre- 

 cludes the possibility that it was formed by the imion of two 

 such eggs. Through treatment with sodium chloride I have 

 I)roduced embryos in which the brain tlifferentiated without 

 closure of the neural folds, l)ut no true double embryos were 

 obtained by this means; moreover in nature it is improbable 

 that unusual chemical influences should affect a single egg. 



It is moi'e likely that the abnormality was brought about b}' 

 mechanical means. A partial separation of the first two blasto- 



