THE TYPICAL FROGS 2631 



in which the toes are somewhat expanded are as aquatic as those in which they are 

 pointed, and species presenting both modifications are included within one and the 

 same genus. The typical frogs are divided into twenty genera, only two of which 

 are noticed in this work. 



Under the general title of water frogs may be conveniently included 

 all the members (some hundred and forty in number) of the genus 

 Rana, to which belongs the common English frog. The distinctive characteristics 

 of these frogs are to be found in the horizontal pupil of the eye; the more or less 

 deeply notched and free tongue; the presence of teeth on the vomerine bones of the 

 palate; the absence of webs in the toes of the fore- feet, and their presence in those 

 of the hind -limb; and the separation of the outer metatarsal bones of the hind-foot 

 by a web, the extremities of the fingers being simple or expanded. 



With the exception of the southern part of South America (where the whole 

 family is unrepresented), Papua, and New Zealand, these frogs have a world-wide dis- 

 tribution. Although the greater majority of the species are probably aquatic during 

 the breeding season, at other times great diversity of habit is displayed by the dif- 

 ferent representatives of the genus, some being aquatic, others terrestrial, and 

 others, again, burrowing, or even more or less arboreal. The existence of burrow- 

 ing habits is indicated by the great development of a tubercle on the inner side of 

 the metatarsus, which in one Indian species (Rana breviceps} has a sharp edge, and 

 is used in a shovel-like manner to excavate the burrow. Such burrowing species 

 are further characterized by the shortness of the hind-limbs, and thus assume a more 

 or less toad-like appearance. Large discs at the ends of the toes usually, on the 

 other hand, are indicative of arboreal habits; although, as already said, smaller discs 

 are met with in certain purely aquatic species. 



Selecting some of the European representatives of the genus for spe- 

 cial mention, we may first notice the edible frog (R. esculenta) charac- 

 terized by the pointed tips of the toes, the smooth under surface of the 

 body, the presence of a. broad glandular fold along the sides, and the marbling of 

 the thighs. Exceedingly variable in coloration, this frog generally has the upper 

 parts olive or bronzy brown, more or less spotted or marbled with dark brown or 

 black; there are generally three light stripes along the back, while the sides of the 

 head and ground color of the flanks are sometimes green; the marbling on the 

 thighs occupying their hinder surfaces, and being black in color. The males are 

 specially characterized by the presence of a globular sac, connected with the produc- 

 tion of the croaking, on each side of the head, opening by a slit behind the angle of 

 the mouth. Inhabiting Europe, Asia as far west as Japan, and Northwestern 

 Africa, the edible frog is common in England, the dark race occurring in the fens 

 of Cambridgeshire, and the green variety in Norfolk. The use of the flesh as food 

 probably led to the introduction of this species into Cambridgeshire by the monks; 

 while the Norfolk colony was imported between 1837 and 1842. From this species 

 the common English frog (R. temporia] is readily distinguished by the incomplete 

 webbing of the hind-feet, and the presence of a dark temporal spot extending from 

 the eye to the shoulder, as well as by the absence of external vocal sacs in the males. 

 Moreover, if the skulls of these two species be compared, it will be found that while 



