AMPHIBIA 203 



Dendrobatinus carry their tadpoles on the back while going from a pool 

 that is drying up to one with plenty of water. 



Sub-Family 3. Ranirwe, comprises the typical frogs, to which our 

 common bull-frog, leopard frog (Fig. 115, E), grass-frog, etc., belong. 

 These common frogs are very well known to every student of zoology 

 and will not be dealt with here. The Raninse are remarkable for the 

 range of their adaptive radiation. They range from purely aquatic 

 frogs like Rana catesbiana (Fig. 115, F), the "bull-frog," to terrestrial 

 frogs like R. temporaria, the European brown frog; from those living 

 on the ground in woods to those living in trees, and even to fairly good 

 flying frogs. These so-called "flying frogs" have fully webbed large 

 feet (Fig. 115, D) with which they parachute to the ground or from 

 tree to tree. There is, however, considerable doubt as to their "fly- 

 ing" ability. Their air leaps cannot be very great, possibly from 20 

 to 30 feet being the maximum. Wallace's exaggerated account of 

 these activities has been too widely accepted. 



The frog's usual method of capturing insect prey is shown in Fig. 

 115, G. Any statement as to special breeding habits would be largely 

 a repetition of what has been said about other groups. 



The Development of the Frog 



The early embryology of the Amphibia is in general the most gen- 

 eralized found among the vertebrate classes, and that of our com- 

 monest frogs is as primitive as can be found. Why the development of 

 the Amphibia is more primitive than that of the fishes is not an easy 

 question to answer. It appears probable, however, that the earliest 

 fishes, such as the lobe-fin ganoids, had a type of egg and a process of 

 development even more like that of the Amphibia than have the mod- 

 ern fishes, and that the amphibian descendants of these ancestral 

 fishes have retained more nearly than the fish descendants the primi- 

 tive features of development. A study of comparative embryology 

 of chordates usually begins with the development of Amphioxus and 

 then proceeds directly to that of the frog. Then follows the develop- 

 ment of the chick, as an example of conditions in the Sauropsida, and 

 finally that of a eutherian mammal. 



The life history of the frog may conveniently be divided into 

 four periods:— 



1. The period of germ-cell formation, which terminates with 

 spawning. 



