232 



BRANCH CHORDATA 



The spotted salamander (Amblys'toma puncta'tum) is our common species 

 in the Mississippi Valley (Fig. 191). It is dark brown or blackish above, 

 marked with about thirty irregular yellow spots. It is found in wells and 

 cellars. It is oviparous. 



One species (Amblys'toma tigri'num), which is found in Mexico and Cali- 

 fornia and even in New York and Minnesota, affords a striking example of 

 neoteny, 1 or the " more or less complete retardation of development, or the 

 retention of partially larval conditions." 2 If the pond in which this axolotl, 

 or larva (Fig. 192), lives begins to dry up, its gills, fins, and tail shrink, and 

 finally disappear, the animal begins to breathe air, and gradually becomes a 

 terrestrial salamander. 3 But if it is reared in deep water or forced by deep 

 walls to remain in aquatic conditions, the larval or aquatic gills and tail 

 are retained, even after sexual maturity has been reached. One would 

 think this was a forcible proof of the influence of environment on the 

 development of the individual, but the strangest part of it is that it is said 



Fig. 191. Common yellow spotted salamander. (Morse.) 



there have sometimes been found, side by side with these prolonged larval 

 individuals, others apparently of the same species which have completed 

 their metamorphosis. 4 



The newts or tritons all prefer moisture without heat. In the mating 

 season they take to the water, undergo various changes, and become 

 aquatic. After the breeding season is over, they become terrestrial, hiding 

 in cracks or in the sand. Some estivate in the hot dry season. They 

 hibernate usually in the ground, but sometimes in ponds. The food con- 

 sists of insects, centipedes, and snails. " They do not drink, but soak them- 

 selves in water." 5 



1 Baskett and Ditmars. 



2 Parker and Haswell. 



3 Linville and Kelly. 



4 Hertwig (p. 587, Kingsley's translation) says adults of true axolotl are 

 unknown. 



5 Gadow, p. 123. 



