THE ANIMAL ORGANISM 



27 



perhaps, one should start with the Protozoa and work up the 

 scale, but practically more rapid and satisfactory progress is made 

 if the beginner starts with a larger animal and one with which he 

 is to a certain extent familiar, such as the leopard frog or grass 

 frog, Rana pipiens, or any other species of frog. The leopard 

 frog is classified as a member of the phylum Chordata, the 

 subphylum Vertebrata, the class Amphibia, the order Salientia, 

 the family Ranidae, the genus Rana, and the species pipiens. It 

 is therefore a member of the highest phylum, Chordata, and also 

 of the subphylum Vertebrata to which Man also belongs. It is 

 an example of a vertebrate animal, which refers specifically to the 

 fact that it has a vertebral column or backbone. 



Fig. 7. — Rana pipiens, sketched from life. 



The leopard frog is found in nature living near ponds, lakes, and 

 streams of fresh water of the North American continent east of 

 the Pacific slope. The winter months are spent in hibernation, 

 during which active feeding ceases and all bodily activities are 

 reduced to a minimum. Several varieties of the species differing 

 from one another in color pattern are known. In the variety 

 illustrated in Fig. 7 the dorsal side of the head and body, and 

 the upper sides of the legs, are marked by large brownish spots, 

 bordered by narrow light iridescent green edges, on a background 

 of lighter brown. The sizes of the spots and the pattern vary in 

 different races. The throat, the ventral side of the body and the 

 inner sides of the legs are whitish and unmottled. 



The skin of the frog is smooth and is rendered slippery by 

 mucus, a viscid secretion poured out on its surface by skin 

 glands. The skin is held loosely to underlying parts by sub- 



