CLASS AMPHIBIA 497 



ficial muscles or those of the head and gills, body wall, and the 

 appendages. Because of the development of the terrestrial limbs, 

 the latter group is much more complicated in this amphibian than 

 it was in the fishes. For the detailed information concerning the 

 specific muscles the student will depend on the accompanying illus- 

 trations and the laboratory study. 



The Nervous System and Sense Organs 



Since this system resembles that of the fish Avhich has been studied 

 already, and is so closely similar to that of the frog, which is de- 

 scribed in the next section of the book, it seems unnecessary to 

 describe it here.* 



THE BULLFROG 



Habitat 



The bullfrog is a solitary animal except during the breeding sea- 

 son. It is strictly aquatic and does not leave the pools as does the 

 leopard frog. It prefers bodies of quiet water where there are both 

 shallows and deeper water, such as lagoons, small lakes, and the 

 cypress ponds of swampy regions. In such a situation, the shore is 

 protected by low willows or other trees, and the shore waters are 

 filled with aquatic plants, pickerel weeds, and floating lily pads. 

 These furnish not only a good hiding place but a good hunting 

 ground for the crayfish, insect larvae, water beetles, snails, and 

 other aquatic organisms which make up the bullfrog's diet. This 

 diet is quite varied and may even include younger frogs. 



Bullfrogs are found in North America east of the Kockies from 

 Canada to Mexico. They have also been introduced into the western 

 portion of the United States and into various foreign countries. 



External Structure 



Bullfrogs obtained in the South and Southwest are usually of two 

 species, Rana catesheiana Shaw, the common bullfrog, or Bana grylio 

 Stejneger, the southern bullfrog. Individuals of the former species 

 attain larger sizes, and the giant bullfrogs of the southern swamps 

 usually are Rana catesheiana. The two species differ not only in size 

 but also in external appearajice, particularly when alive. However, 

 they are essentially the same anatomically, and this chapter is based 

 on a study of Rana catesheiana. 



•Illustrations of this system mav be found in Stuart: Anatomy of Necturus 

 maculosusj Denoyer-Geppert Co., Chicago. 



