250 GENERAL ZOOLOGY 



coloration. Necturus is sometimes called a "mature 

 larva" and it may be properly compared with the well- 

 grown tadpoles of many other amphibians. The gills are 

 functional, but lungs have developed and the sexual organs 

 are mature. 



GENERAL REMARKS ON CAUDATA 



The tailed amphibians show an interesting transition 

 from aquatic to terrestrial habits. Necturus is entirely 

 aquatic, possessing well-developed gills and very small 

 lungs. Siren, which lives in the rivers of the southeastern 

 United States, starts in life as a tadpole, partly loses its 

 gills, and then has them enlarge again to functional size. 

 Cryptobranchus is aquatic throughout life and breathes by 

 means of gills which, however, are covered. Water for 

 respiration enters the mouth and passes out through a pore 

 on either side of the neck. Ambystoma is the common 

 " tiger" salamander throughout the eastern and central 

 United States. It is of particular interest because certain 

 species in the genus show psedogenesis; that is, they be- 

 come sexually mature while in the larval state, and an 

 individual with gills may lay fertile eggs. As a rule, how- 

 ever, the adults are found in damp situations on land, 

 and are often encountered under stones and logs, or in 

 cellars. Diemyctylus is the beautiful vermilion-spotted 

 newt of New England. Its life cycle requires several years 

 for completion. During the first three years it is a green 

 aquatic larva; then migrates to the land and becomes 

 bright orange with vermilion spots. After a period of 

 terrestrial life, the newt returns to the water, becomes 

 green in color, and leads an entirely aquatic existence while 

 breeding. Desmognathus is a truly terrestrial salamander 

 which has no gills or lungs, but breathes by gulping air 

 into the throat, which is very vascular. After becoming 

 mature it returns to the water to breed. Plethodon, the 

 red-backed salamander, does not enter the water even to 



