62 



INTRODUCTION. 



in Ran a, or slit-like, and situated at the side of the 

 tongue, as in most other genera. Pelodytes and Hyla 

 have two openings, whilst Bitfo has commonly but one, 

 either on the right side or on the left. 



In Bombinator igneus internal vocal sacs are well 

 developed, but are formed by the skin of the floor of 

 the mouth, which is loose and plicate, and projects 

 through a slit dividing the submaxillary muscle into 

 an anterior and a posterior portion. Diseoglossus has 

 rudimentary vocal sacs of the same type, but they are 

 confined to the sides of the throat, near the mandible. 

 Bombinator pachypus, Alytes, Pelobates, Bufo vulgaris, 

 and Bana grseca, latastii, ibcriea, and agilis lack the 

 vocal sacs. 



The mode of inflation of the vocal sac is best 

 observed in Hyla arborea, the bladder-like appendage 

 when blown being of enormous size, nearly as large 

 as the body, which, when the animal croaks, is much 



Fig. 24. 



Hyla arborea, $ , with the vocal sac in the collapsed and inflated 



conditions. 



thinned by the emptying of the lungs, as shown in 

 the accompanying figure (Fig. 24). This mechanism of 

 the shifting of the air from the lungs into the throat, 

 and vice versa, explains the fact, paradoxical in appear- 

 ance, of Batrachians being able to croak under water. 

 The voice varies very considerably according to the 

 species, and the names bombina, sonans, eampanisona, 

 ridibunda, cachinnans, &c, convey the impressions 

 made on the ears of the earlier observers. It affords 

 the trained collector one of the surest means of ascer- 



