THE VERTEBRATES 201 



the most familiar batrachians in our study of the toad and 

 frog (Chapters III and IX). Other familiar members of 

 this class are the salamanders. All batrachians breathe by- 

 means of gills for a longer or shorter time after birth. But 

 except in very few cases these gills are lost and lungs de- 

 veloped so that the adults cannot breathe under water. The 

 toads and frogs are closely related, and have about the same 

 life-history and habits, except that the fully-grown toads live 

 on land instead of in and about ponds. In structure toads 

 differ from frogs in having no teeth. There are only a few 

 toad species in North America, but one of these is very 

 abimdant and widespread. It appears in two or three 

 varieties, the common toad of the Southern States differing 

 in several particulars from that of the Northern. The toad 

 is a familiar inhabitant of gardens, and does much good by 

 feeding on noxious insects. It is most active at twilight. 

 Its eggs are laid in a single line in the center of a long, slender, 

 gelatinous string or rope, which is nearly always tangled and 

 wound round some water-plant or stick near the shore on 

 the bottom of a pond. The eggs are jet black, and when 

 freshly laid are nearly spherical. At the time of the egg- 

 laying the toads croak or call, making a sort of whistling 

 sound, and at the same time pronouncing deep in the throat 

 "bu-rr-r-r-r." The toad does not open its mouth when 

 croaking, but expands a large sac or resonator in its throat. 

 The toad tadpoles are blacker than those of frogs or sala- 

 manders, and undergo their metamorphosis while of smaller 

 size than those of frogs. When they leave the water they 

 travel for long distances, hopping along so vigorously that in 

 a few days they may be as far as a mile from the pond where 

 they were hatched. They conceal themselves by day, but 

 will appear after a warm shower; this sudden appearance 

 of many small toads sometimes gives rise to the false notion 

 that they have fallen with the rain. 

 There are about a dozen species of frogs in the United 



