192 VERTEBRATE ZOOLOGY 



white, the under side yellow with black spots, and the side of the tail 

 has a broad bluish-white band. The female has quieter colors, a gen- 

 eral brownish-black ground with a yellow line down the middle of the 

 back. This is the most pronounced instance of sexual dimorphism 

 among the Urodela and possibly within the class Amphibia. The 

 crested newt has a wide distribution, occurring in England and Scot- 

 land and through Central Europe. Many other species of the genus 

 Triton occur, two of which, T. torosus and T. virescens, occur in North 

 America, the latter being common through the Eastern United States. 



Family 3. Proteidce. The Mud-Puppies. — These animals have 

 three pairs of fringed external gills throughout life (perennibranehi- 

 ate); both fore and hind limbs are present; eyes are without lids; 

 maxillaries are absent; teeth occur on premaxillaries, vomers, and man- 

 dible; vertebrae are amphicoelous. Only three genera, each repre- 

 sented by a single species, occur, two in America and one in Europe. 



Nedurus maculatus (113, A) is the common American "mud-puppy," 

 so called because the fringed gills look something like the pendant 

 hairy ears of a water spaniel. They are found all over the eastern 

 part of the United States and in eastern Canada. They are about a 

 foot in length, of a muddy-brown color, mottled with blackish spots. 

 Behind the dark red external gills are paired gill-clefts. These am- 

 phibians impress one as rather dull, stupid animals, living a sluggish 

 life on the muddy bottoms of lakes and rivers. At times, however, 

 they move about quite smartly with graceful eel-like motion. They 

 are active chiefly at night, when they swim about in search of frogs, 

 Crustacea, worms, fishes, and insects. They are often found in very 

 cold water and seem to be well adapted to low temperatures. In 

 general it may be said that these animals resemble closely the larvse 

 of the Salamandridse, especially that of Amblystoma (Axolotl); 

 a fact that has given rise to the idea that they are not truly primitive 

 aquatic Amphibia at all, but simply a species that, after possibly 

 thousands of years of psedogenetic habit, has lost its plasticity and is 

 no longer able to metamorphose from the larval to the adult condi- 

 tion. It would be interesting to try thyroid feeding experiments 

 upon the larvse with the idea of inducing metamorphosis into a true 

 adult type. 



Proteus anguineus (Fig. 113, B), "olms" as the Germans caU them, 

 are blind cave mud-puppies. The whole body is white or nearly so. 

 If kept in places where light is not absolutely excluded they become 



