8 



THE BIOLOGY OF THE FROG 



CHAP. 



Ann Arbor, Michigan, at the following dates : March 15, 

 1892 ; March 26, 1895 > March 29, 1896 ; March 13, 1897 ; 

 March 28, 1905. 



The larvae of A. tigrinum were formerly considered a 

 separate species, the axolotl, which was placed in a distinct 

 genus, Siredon, among the perennibranchiate urodeles. 

 Under certain conditions the external gills of this larva 

 may be retained until after the breeding season, and this 

 peculiarity led to its being mistaken for a normal adult 

 form. It has been contended that the metamorphosis of the 

 axolotls could be accelerated if they were forced to breathe 

 air, but Professor Powers has recently shown that the factor 

 of nutrition is probably the most important one, although 

 others are influential, in producing this change, since it 

 usually follows in sufficiently mature larvae upon a sudden 

 diminution of the food supply. 



The Desmognathinae include three genera, of which 

 Desmognathus is the most common. It contains only three 



species, all of which 

 are confined to the 

 eastern part of the 

 United States. The 

 species live con- 

 cealed in the day- 

 time under stones 

 or in sheltered nooks 

 where the air is 

 moist. The female 

 of D.fuscus lays her 

 eggs in two long 

 strings which she wraps around her body after having resorted 

 to a suitable hiding place. Another representative of this 

 subfamily is Typhlotriton spelceus, a blind species found in a 

 cave in Missouri. 



FlG. 4. — Desmognathus fuscus. Female with 

 egg-mass. (After Wilder.) 



