ADAPTATIONS AND DISTRIBUTION 



eventually, tadpoles ot' at least three ages were developing simultaneously. 

 Close watch was kept of this pool till midsummer when all water had dis- 

 appeared through evaporation. The tadpoles of the first breeding congress 

 were large enough belore other eggs were laid to distinguish them at a glance 

 from the younger individuals. The pool was originally tormed in April and 

 the last tadpoles metamorphosed in late June. During May the weather grad- 

 ually warmed, until by June 1 and thereafter water temperatures in early 

 afternoon were quite high (30°-35° C.) and on exceptionally warm days 

 even higher. We are principally concerned here with those tadpoles which 

 resulted from the first breeding congress. 



Metamorphosis of these tadpoles was finished as follows: (1)5. hurteni, 

 on the twenty-first day after eggs were laid.' At this time young were found 

 on the bank and no tadpoles could be captured with a dip-net in the water; 

 (2) M. c. olivacea on the twenty-eighth day (first young out of the water on 

 the twenty-sixth); (3) B. t. americanus , on the thirty-first day (first young 

 on the eighteenth); (4) H. v. versicolor, on the forty-first day (first young 

 on the thirty-ninth); (5) Ps. strccl^cri. on the forty-eighth day (first young 

 on the fortieth); and (6) /?. berlandicri, on the sixtieth day (first young on 

 the fifty-third). Tadpoles of this species grew exceptionally large before meta- 

 morphosis in this pool and several of them died without metamorphosing, 

 probably because of too high temperatures in the pool or from lack of oxygen. 

 That it was temperature is indicated by the facts that when the water at the 

 pool's edge approached 35° C. all sought deeper and cooler portions of the 

 pool; and further, that there was little of the rising to the surface to gulp 

 air that I have often observed in other pools. It should also be noted that at 

 no time did other tadpoles show distress and that only a few even of the 

 frogs were involved, something not to be expected if lack of oxygen were 

 the primary operating factor. During the same time, another pool of inter- 

 mediate character nearby was also under observation. (Fig. 29.) In it, B. t. 

 americanus, Ps. strec/{eri, and H. v. versicolor which metamorphosed by June 

 1 came through beautifully and hundreds emerged. But younger individuals 

 on this date soon began to die and very few succeeded in metamorphosis. 

 There were no frog tadpoles in this second pool with which to compare those 

 in the first. Such observations as these have been made sufficiently often dur- 

 ing the past six years to warrant the following conclusions: (1) Intrinsic 

 specific developmental rates are the rule among Oklahoma frogs and toads. 



(2) Metamorphosis is hastened in all species observed'' except R. berlandieri 

 (see infra) by higher temperatures under comparable natural conditions. 



(3) In general, members of the genus Scaphiopus lead all others in develop- 



" That there !;> an innate protoplasmic factor is especially apparent from observations 

 on the early development of Scaphiopus. This is not based merely upon a rapid rate of de- 

 velopment of the tadpoles but goes back to the embryonic stages, at least in S. homhifrons. 

 This was observed by Trowbridge and Trowbridge, 1937, who reported a fast cleavage rate 

 2s compared to the usual conditions in North American Salientia. 



^ R. berlandieri and H. v. versicolor are the only ones of their genera observed suf- 

 ficiently from this point of view. Insufficient observation has also been made on Pi. triseriata, 

 B. insidioy, and B. ptiiutatiis to warrant generalization. 



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