164 ELEMENTARY BIOLOGY. [CHAP. 



presented merely by the pointed end of the body; the gape 

 elongates until the angle of the mouth lies behind the eye, 

 instead of a long way in front of it, as in the tadpole; the 

 labial membrane and the horny armature of the mouth 

 disappear, while teeth are developed in the upper jaw and 

 on the vomers ; the intestine becomes less and less coiled as, 

 not growing at the same rate as the body, it becomes rela- 

 tively shorter; and the animal gradually changes its diet 

 from vegetable to animal matters the perfect Frog being 

 insectivorous. 



The two species, Rana temporaria and Rana escuknta, 

 are distinguishable by the following external characters. In 

 Rana temporaria, the interspace between the eyes is flat or 

 slightly convex, and its breadth is usually greater than, or 

 at least equal to, that of one of the upper eyelids. The 

 diameter of the tympanic membrane is less than that of the 

 eye, often much less. The horny elevation on the outer side 

 of the pes is small or absent, and that on the inner is 

 flattened and has a rounded margin. A patch of dark 

 colour extends from the eye backwards over the tympanic 

 membrane. The males have the cushion on the radial side 

 of the manus black, and they are devoid of vocal sacs. 



In Rana esculcnta, on the other hand, the interspace be- 

 tween the eyes is usually concave and narrower than the 

 breadth of one of the eyelids. The diameter of the tym- 

 panic membrane is as great as that of the eye. The horny 

 elevation on the inner side of the pes is elongated, com- 

 pressed and brought to a blunt edge, so as almost to resem- 

 ble a spur, and a small outer elevation is constantly present. 

 There is no patch of colour at the sides of the head, such 

 as exists in Rana temporaria, and the cushion of the inner 

 digit in the male is not black. The males have a large 

 pouch on each side of the head, behind the angle of the 



