AMPHIBIA 



209 



the winter in the larval stage, and one species of the Ainbly- 

 stoma, the Axolotl, continues throughout life in the larval 

 state, unless forced to terrestrial habits by the drying up 

 of the water. In the Anura, metamorphosis to the adult 

 state involves the absorption of the gills and the tail, and 

 the development of lungs, and an exchange of animal for 

 a vegetable diet. After the first few days of larval life, 



FIG. 242. Frog with the left side cut away and some of the organs pulled down- 

 ward, a, aorta leading from the ventricle ; 6, bladder ; c, spinal cord sur- 

 rounded by the vertebral column of bone ; d, small intestine ; e, opening of the 

 lungs into the pharynx ; h, ventricle of the heart ; k, kidney ; I, lung ; Jiv, liver ; 

 n, brain ; ov, ovary ; ovd , oviduct ; p, pancreas ; r, rectum ; sp, spleen ; st, 

 stomach ; t, tongue ; si, small intestine ; tt, left auricle ; ur, ureter ; v, vena 

 cava ; vc, body of vertebra. 



the frogs and toads do not have external gills like the sala- 

 manders, but the gills are on arches and covered similar to 

 those in fish, but only one opening exists, and that is a small 

 one on the left side just behind the head. 



Dissection. Those wishing to study the structure of 

 this class by making a careful dissection may use any of 

 the salamanders, a large tadpole, or a frog, which can 



