Introduction 



Watch a tree frog leap, catch a swaying branch with pre- 

 cision of aim, and balance itself perfectly on the frail support. 

 See the toad that has jumped to the top of the aquarium bal- 

 ance itself for a few minutes on the edge of the thin glass while 

 it makes an examination of the surroundings before proceeding. 

 Watch a frog that is sitting on some support adjust itself as you 

 tip the support now in one direction and now in another. These 

 actions look as wonderful as the feats of a rope-walker. They 

 are, however, automatic actions, and could be done by a frog 

 whose brain had been removed. The frog has a nervous sys- 

 tem that makes most delicately co-ordinated muscular response 

 through an elaborate system of reflex actions. 



Frogs and toads are sensitive to various forces in their en- 

 vironment and give response according as they are acted upon 

 by these forces. For instance, the earth's gravity affects the 

 tree frog so that it is not at ease unless its head is uppermost. 

 Watch the frog turn again and again in desperate effort to keep 

 its head uppermost when its support is alternately held upright 

 and reversed in position. 



On a warm day the frogs are in full view among the late 

 vegetation of the pond. The next day, after a drop in temper- 

 ature, not a frog can be found. Frogs in captivity remain out 

 of the water or sit with head and shoulders protruding until the 

 air becomes colder than the water. At this time they disappear 

 and lie with flattened bodies and lowered heads at the bottom 

 of the aquarium until a return of higher temperature. Thus 

 frogs give automatic response to temperature stimuli. 



The frog's method of eating is attended with much nervous 

 alertness, and sometimes with unsatisfactory results to the frog. 

 The food consists, in general, of living worms and insects, which 

 are seized and swallowed alive. The frog uses his hands to help 

 put the food into his mouth. The mouth has the sense of touch 

 highly developed, but the sense of taste is present in only small 

 degree. In all cases, movement of a small living object gives 

 the visual stimulus, and, psychologically speaking, brings to the 

 frog the suggestion of something to eat. Long experience of the 

 race has taught that only immediate and swift motor response 

 will result in capture of the food — the miller or grasshopper 

 may take wing, the slug disappear under a board, or the cater- 

 pillar roll into a ball and "play dead." Usually, the result of 



28 



