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EVOLUTION OF ANIMALS 



Part V 



Fig. 34.3. Two of the largest salamanders in North America. Left, the "mud 

 puppy" (Necturus), one foot long, has gills throughout life. Common in eastern 

 rivers of United States and Canada. Right, the hell-bender (Cryptobranchus) , 

 about a foot and a half long; the adult has no external gills but makes up for 

 this by loose folds of skin that function as gills. Hell-benders are usually in the 

 shallows of streams and are secretive, but once seen are not forgotten. 



larvae transform and climb on land as air breathers. But in some localities, 

 such as Mexico, western Texas, the southwest, and Colorado, and under cer- 

 tain special conditions, they continue to grow to full size in the water, become 

 sexually mature but do not change their form or lose their gills (Fig. 34.4). 

 In such a phase they are known as axolotls. 



The best-known North American newts are the "water dog" {Triturus 

 torosus), eight inches long, of the Pacific drainage, and the spotted newt (Tri- 

 turus viridescens) , half as long, of the Atlantic drainage. The "red eft" or "red 

 lizard" of the woods and the spotted newt of the ponds are the same animal 

 in different color phases (Fig. 34.5). Adult spotted newts live in ponds and 

 meandering streams from September or October to the next summer, perhaps 

 longer. The breeding season is in the spring, when an elaborate courtship pre- 

 cedes the egg-laying and lasts from several hours to a day or more, as readily 

 in aquaria as in a pond. After the pair separates, the male deposits white 

 jellied spermatophores containing spermatozoa, on submerged leaves and 

 sticks. As he moves away from a spermatophore, the female creeps over it and 

 takes it into the cloaca, the cavity through which the eggs must pass to be 

 fertiUzed and laid. Upwards of a hundred are deposited separately here and 

 there, usually on submerged plants. The larvae live in the water until toward 

 fall. Then their gills gradually shrink; they acquire lungs, their skin becomes 

 firmer; and their color changes from green to orange-red. They climb out of 

 the pond and spend at least one winter and summer on land, during which they 

 are the red newts of the woodland carpet. In some localities, they return to the 

 water in the fall, as nearly mature animals, their backs turning olive green with 



