DICHOTOMY. 



119 



spring of 1879 he had in an aquarium two or three 

 thousand eggs of A mblystoma punctatum for the purpose 

 of studying their development. One day he chanced to 

 find one with the medullary folds nearly completed, but 

 they had not united at the cephalic end, and appeared to 

 be much rounded at their anterior ends, instead of having 

 the ordinary vague outlines ; he kept it apart, therefore, 



FIG. 65. A two-headed Foal ; anterior dichotomy. 



and watched it. Each free portion of the medullary fold 

 developed a perfect head, which, at first partly united, 

 became gradually more so, until they were connected 

 throughout their entire length. Posterior to the heads 

 there was no sign of duplicity. 



In this case a two-headed monster, with a regular 

 symmetrical body, was developed from one egg, and 



