

XIII.] THE FROG. 157 



the vomers; the intestine becomes less and less coiled as, not 

 growing at the same rate as the body, it becomes relatively 

 shorter; and the animal gradually changes its diet from 

 vegetable to animal matters the perfect Frog being insecti- 

 vorous. 



The two species, Rana temper aria and Rana esculenta, are 

 distinguishable by the following external characters. In 

 Roma temporaries, 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 o'f 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 esculenta, 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 resemble 

 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 jaw, 

 communicating with the cavity of the mouth, and, when 

 they croak, these pouches becoming dilated assume the form 

 of spherical sacs. 



Having thus become acquainted with the general character 

 and life-history of the Frog, and with those features of its 



