38 



BREEDING HABITS OF AMPHIBIA 



These frogs breed in ponds, in wooded regions where there are dead leaves and mud. 

 They begin breeding in early March in water at about 1 2°C. The eggs are larger than 

 those of Rana pipiens (about 2. mm. ) and number about 3, 000. E 

 pending upon the temperature, metamorphosis is reached in from 

 to 50 days. Development is normal even at 4 C. , indicating wide 

 temperature tolerance but at a lower level than for Rana pipiens. 

 Stage #12 to gill circulation stage requires only about 95 hours at 

 15°C. and at 20°C. metamorphosis is achieved in 45 days. 



Exceptional cases of cross-oviposition 



Noble and Aronson (1942) report that when Rana clamitans or Rana 

 sylvatica males assume the amplectic position with ovulating Rana 

 pipiens females, the grip is lateral and below the axillae rather than 

 ventral, as with pairs of Rana pipiens. This grasp seemed to make 

 it difficult for the female to oviposit and the caudal half of the male's 

 body tended to float away from the female. Even though the cloacae 

 are not approximated (see figure below) the eggs are not generally 

 fertilized or, if fertilized, rarely develop beyond the gastrula stage 

 in hybrid crosses. 



Female Rono pipiens ovipositing with male Rana clamitans 



(Drawing made by the Illustrators Corps of The American 

 Museum of Natural History. Loaned through courtesy of 

 L. R. Aronson. ) 



TOADS 



Rana sylvatica, 

 the wood frog. 



(Courtesy C. H. Pope 

 1944: Chicago Mus. 

 Nat. Hist.) 



BUFO AMERICANUS , the American toad. This toad, common in gardens as a night, 

 prowler, is found in the northeastern United States. The adults vary in size from 2 to 4 

 inches in body length, the males being smaller and possessing black chins. The ventral 

 surface of these toads is sand colored and granular while the dorsal surface is warty. 

 The eyes are protruding and two large parotid glands extend backward from the eyes. 

 The color is olive green. Food consists primarily of large insects found around gardens. 



Breeding occurs in April and May, the egf^s being layed in long spiral tubes of jelly and 

 totalling up to 20, 000 in exceptional cases. The average is about 6, 000. The time nec- 

 essary for hatching is 2 to 17 days, depending upon the temperature, and for metamor- 

 phosis in nature is about 60 days and occurs in August. The temperature tolerance is 

 from about 50°F. to 86°F. 



