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Biology in America 



sary to follow the feats of the imagination performed by the 

 morphologists in leaping the gap between Hydra and higher 

 animals. Suffice it to say that an imaginary ancestor has 

 been created to serve as the starting point of the latter, from 

 which these have diverged, each upon its several way. 2 



A SERIES OF VERTEBRATE EMBRYOS 



I, II, III, 1st, 2nd, and 3rd stage. From Eomanes ' ' Darwin and 

 After Darwin. " 



By permission of the Open Court Publishing Company 



If one compare a series of the early stages of animals, which 

 in the adult form are widely different from one another, he 

 may find it difficult or impossible to tell them apart. The 

 embryos of fish, frog, bird and mammal are almost identical 

 with one another at a certain stage of development. 



2 The above statement must not be interpreted as an oversight of 

 the higher crelenteratcs and the ctenophores. But even taking a 

 ctenophore as a " jumping off point" there is still a wide and as 

 yet unfathomed abyss to cross. 



