THE AMPHIBIA OF OKLAHOMA 



dead tadpoles which functions to hasten metamorphosis in oncoming gener- 

 ations is not known. Hypothetically, a substance of this kind is strongly sug- 

 gested by the observations in Pool C where the fastest developmental rate 

 known has been seen ( Bragg, 1948). Further progress seems to lie in search- 

 ing for this hypothetical substance and, if found, in determining its source. 



It should be noted that the usually observed differences in behavior of 

 tadpoles of S. bombijrons and S. hiirterii, so puzzling when first noted, seem 

 to be merely a matter of breeding site, selected by the respective adults. It has 

 been stated earlier (Bragg, 1944-45) that S. bombijrons always utilizes 

 deeper water than S. hurterii, if available. When tadpoles of S. bombijrons 

 do occur in shallow pools, especially of type 1, they show the same behavior 

 as S. hurterii. 



The total observations, therefore indicate the general conclusion that, 

 in at least two species of spadefoots, all phases of reproductive activity of the 

 adults (including the xeric breeding pattern) and the behavior of tadpoles 

 in any one pool (including social aggregation of several types and canni- 

 balism at times) are phases in a nice adjustment tending to secure the sur- 

 vival of the greatest numbers of tadpoles, on the average, under the adverse 

 conditions of their environment, the dry grasslands and savannahs of the 

 West. 



Literature Cited 



Ball, Stanley R. 1936. The distribution and behavior of the spadefoot toad in Connecticut. 

 Trans. Conn. Acad. Arts and Sci. 32: 351-379. 



Bragg, Arthur N. 1944. Breeding habits, eggs and tadpoles of Srap/iiopiis litirteni. Copeia 

 4: 230-240. 



. 1944-1945. The spadefoot toads of Oklahoma with a summary of our knowledge 



of the group. Amer. Nat. 78: 517-533, continued 79: 52-72. 



. 1945. Breeding and tadpole behavior in Scapliioptts hurterii near Norman, Okla- 

 homa, spring, 1945. The Wasmann Col. 6: 69—78. 



. 1946. Aggregation with cannibalism in tadpoles of Scaphiopus homhijrons with 



some general remarks on the probable evolutionary significance of such phenomena. 

 Herpetologica 3: 89-96. 



1948. Adtlitional instances of social aggregation in tadpoles. The Wasmann Col. 



7: 66-79. 

 Bragg, Arthur N., and Chas. C. Smith. 1943. Observations on the ecology and natural 



history of Anura IV. The Ecological distribution of toads in Oklahoma. Ecology 24: 



286-307. 

 Trowbridge, A. H. and Minnie S. Trowbridge. 1937. The cleavage rate in Scciphioptts 



homhijrons Cope with additional remarks on certain aspects of its life history. Amer. 



Nat. 71: 460-480. 



ii6 



