2 /. H. Pozvers 



question. But here I found, almost from the start, that, whatever 

 the true causes might be, my observations were negativing or 

 greatly modifying their conclusions. And it was first as a conse- 

 quence of this that I began systematically to collect facts and 

 verify apparent conclusions. In this paper I shall present a state- 

 ment of some of those results, together with such illustrations as 

 space will permit, deferring to some future opportunity the 

 arrangement of my material in more detailed, complete, and sta- 

 tistical form. 



It will be interesting to begin by stating the general view of 

 Baird and Cope as expressed in Cope's work on the Batrachia of 

 North America. The general view there expressed, as to .the 

 nature of nearly all the individual variations in A. iigrinum, is that 

 they are the result of variations in the time and the degree of, i. e. 

 the completeness of, metamorphosis. No experimental evidence 

 is adduced, but the assumption seemed to the writers to agree 

 well with the character of the variations themselves. Sometimes 

 it is made with reference to the conditions of the whole individual 

 animal; more frequently it is invoked to explain some single or 

 a few eccentric features. Thus differences in general body pro- 

 portions, in the length and form of the tail, in the width and form 

 of the muzzle, the development of the tongue and the palatal 

 teeth are all ascribed, in one way or another, to varying degrees 

 of "embryonic tendency," i. e. to the partial retention of one or 

 more larval characters. 



As the external cause of these variations Cope assigns differ- 

 ences in season and temperature, varying with varying geograph- 

 ical habitats. "Specimens from New Jersey are almost always 

 more fully developed than those from western regions ; the former 

 is a warmer district, than the latter." He adds, however, that "of 

 two specimens from New Orleans only one exhibits the denti- 

 tional characters of the New Jersey individuals." 



A second group of variations, such as the depression of the 

 digits, compression of the tail, etc., are assigned by the above 

 writers to the direct influence of .the environment ; in the cases of 

 the organs mentioned, to the persistence of the aquatic habit in 

 adults. 



198 



