RAN A. 269 



the sac actually developed, although smaller than in 

 the males. 



Fig. 99. 



<< K 



Lower view of head of male, showing 

 inflated vocal sacs. 



Variations. — It is a well-known fact that the edible 

 frog presents a greater amount of variation, both as 

 regards structure and coloration, than perhaps any 

 other species of Batrachians. No herpetologist having 

 before him the Japanese and Spanish frogs, without 

 a knowledge of the intermediate forms, would hesi- 

 tate to pronounce them as representing different 

 species ; they have, in fact, been referred to distinct 

 genera by such experienced workers as Peters and 

 Cope. But if we pursue our investigations over the 

 wide area occupied by this frog, viz. the whole of the 

 Pala3arctic region, we soon find all the differences by 

 which we were at first struck to blend through such 

 a number of intermediate forms as to leave no other 

 course open but to maintain intact the Linnean species. 

 However, a great difficulty still remains to be dealt 

 with : the principal of the differences ascertained are 

 not merely individual ; nor are they entirely dependent 

 on locality or climate, as almost identical specimens 

 are met with at such distant points as North Germany, 

 the Sahara, and Baluchistan. And, what is more 

 striking still, in the case of two forms occurring in 

 the same locality they may be perfectly separable 

 and not interbreed, as has been shown to be the case 



