AMPHIBIA 199 



ready to hatch he betakes himself to the water for the period of 

 hatching. 



Family 2. Pelobatidce. The tongue is oval, hitched in front but 

 free behind, so that it can be thrown out; upper jaw and vomers with 

 teeth ; vertebrae procoelous. There are seven genera consisting of about 

 20 species. Pelobates cultripes (Fig. 114, D), the " spade-foot toad/' is 

 the best known of the family. They are typically burrowing toads, 

 digging rather deep holes in sand and resting there during the day. 

 The " spade" is a modified hind foot, which has a strong spur (Fig. 114, 

 E) on its under surface which aids in digging. The species are noc- 

 turnal in feeding habits. 



Family 3. Bufonidce. The Common Toads. They have no teeth in 

 upper or lower jaws; vertebras procoelous and without ribs. They 

 are for the most part decidedly terrestrial, some of them occupying 

 arid territory. 



Bufo vulgaris (Fig. 114, F and G), the common toad of North Amer- 

 ica and other palearctic regions, is typical. The color is variable and 

 changeable, highly protective in its resemblance to the background. 

 They are nocturnal in habits, feeding on worms, insects, and snails. 

 One sees them frequently under electric lights waiting for dazed in- 

 sects to drop to the ground. They hop quickly to the fallen insect and 

 snap it up suddenly. Earthworms are crushed and squeezed till 

 comparatively quiet before swallowing occurs. In the daytime toads 

 hide under stones or in dark corners. They breed in temporary pools 

 in the early spring. The newly hatched toads are surprisingly small 

 and require nearly five years to reach maturity. 



Toads are almost without enemies on account of their noxious skin 

 secretions. About the only agency in keeping down their numbers 

 appears to be parasites and epidemics of disease. 



Family 4- Hylidce. (Tree-Frogs or Tree-Toads.) Upper jaw and 

 vomers with teeth, lower jaw also toothed in one species Amphig- 

 nathodon; vertebrae proccelous without ribs; fingers armed with ad- 

 hesive pads; tongue protrusible to varying degrees. They are all 

 climbing arboreal frogs, many, but not all, being green in color. They 

 are very widely distributed and have in all about 150 species; hence 

 this is one of the largest families. The genus Hyla is the most gener- 

 alized and wide-spread genus. H. versicola (Fig. 115, A) is the com- 

 mon tree-toad of the Northern United States. It emits a " clear, loud, 

 thrilled rattle" quite familiar to most naturalists. These tree-toads 



