12 . THE BIOLOGY OF THE FROG chaj. 



of this group is the pecuHar Surinam toad, Pipa americana, 

 from the northern part of South America. This creature 

 has a most grotesque appearance. The back is broad and 

 flattened, the head small, triangular, depressed, and fur- 

 nished with irregular flaps near the lips ; the eyes are small 

 and have a round pupil. The most remarkable feature of 

 the species is the mode in which the female carries the eggs 

 and young. After the eggs are laid and fertilized, they be- 

 come pushed upon the back of the female, to which they 

 adhere. The skin then grows up around the eggs, inclosing 

 them in separate cavities which become entirely covered 

 over. The tadpole stage is passed within these cavities. 

 When the young Pipa is quite fully formed, it breaks out and 

 makes its escape. 



The Liscoglossidae are not represented by any American 

 species. One of the most noteworthy of the European 

 species of this family is the so-called obstetrical toad, Alytes 

 obstetricans. In the breeding season the male clasps the 

 female in the usual way, and when the egg strings are ex- 

 truded, he tangles them around his hind legs and carries 

 them about with him. When the young larvae are about 

 ready to escape, the male takes to the water and frees him- 

 self of the mass. 



The Pelobatidae include but two American genera, 

 Scaphiopus and Spea. These forms are commonly known 

 as the spade-foot frogs, on account of the peculiar horny 

 appendage which occurs on the inner side of the hind foot. 

 This structure is employed in digging in the ground, where 

 the animal is concealed during the day. Scaphiopus hoi- 

 hrooki, which is found in the southern and eastern parts of 

 the United States, is very capricious in making its appear- 

 ance. After rains in the spring or summer the spade-foot 

 frogs come out in great numbers and lay their eggs, making 



