;>24 Illinois State Latjoralonj of Natural Histonj. 



The species occurs in abundance throughout Illinois. 

 Dunleith (Ridgvvay), Freeport, Cook Co. (Kennicott), Green 

 R., Henry Co., Normal, Peoria (Brendel), Cairo, Grand Detour 

 (Yarrow). 



This frog can generally be distinguished from its near 

 ally, 7?. paJiistris, by the shape of the spots on the back, by the 

 equal size of the three spots on the head, by the narrower and 

 more elevated glandular folds, and by. the ground color above, 

 which is green, brassy, or greenish gray, instead of brown. As a 

 rule, this species has less black about the tympanum. Speci- 

 mens are occasionally found which are nearly intermediate be- 

 tween the two species, arid the young especially are often very 

 similar. There still exists a difference of opinion as to whether 

 or not the males of B. pipiens have external vocal sacs. The 

 fact is that the vocal sacs are as truly external in E. palustris 

 and R. pipiefis as they are in L'. utricularia (li. berhmdieri, etc. 

 of authors), and the difference between the two former and the 

 two latter, in respect to the sacs, is that the skin behind the angle 

 of the mouth is conspicuously distended to accommodate the sacs 

 in T\. /ifricidaria, and is not thus expanded in the other two 

 species. Of the many males of E. pipiens which have been ex- 

 amined from central Illinois none have the skin distended, but 

 all have sacs just beneath the angle of the mouth between the 

 skin and adjacent muscles. The species has been described as 

 having internal vocal sacs, but the latter occupy the same po- 

 sition as in It. utricularia.^ and differ only in being smaller. 

 Next to the bull frog, this is our most familiar species. It oc- 

 curs everywhere along brooks and about ponds, and in damp 

 weather may be found in fields at a considerable distance from 

 water. During the dry weather in August it collects in great 

 numbers about pools of water on the prairies. Its food con- 

 sists of insects and, at least occasionally, of mollusks. In the 

 few stomachs examined by the writer, Coleoptera constituted 

 the principal part of the former. The mollusks were taken 

 from the stomach of a single specimen and belonged to the ge- 

 nus Limiiii'a. 



