Chapter 5 



THE LIFE OF THE JUVENILE FROG 



In tliis chapter, I have the rather difficuk task of dealing with a phase 

 of this animal's hfe that is very little known, namely, the stage that 

 begins with metamorphosis and ends with sexual maturity. 



Metamorphosis 



This is a well-worn theme in its embryological and physiological 

 aspects, but for the ecologist there is little information. In some species, 

 for example B. hufo (Savage, 1952) the tadpoles collect in a large 

 aggregation at the bottom of the pond, shortly before they meta- 

 morphose. The function of this habit is unknown, and it docs not 

 seem to happen in JR.. temporaria, which seems simply to remain near 

 the edges of the pond until it is sufficiently developed to emerge from 

 the water. I have already recorded a case of heavy mortahty at this 

 time, apparently due to drowning, just as can be seen in captivity if 

 the animals are kept in a vessel with sides too steep for them to chmb. 

 It is remarkable that frogs of this age seem to drown so easily. It is 

 well known that the cutaneous respiration of frogs is sufficient to 

 maintain life, provided that the water in which the frogs are immersed 

 is well oxygenated. Metamorphosis in nature occurs in the hot weather, 

 and perhaps this is the reason for the dependence of the young frogs 

 upon aerial respiration. 



Dispersal 



There are numerous reports of immense numbers of little frogs 

 leaving ponds at this time, and, indeed, almost supernatural explana- 

 tions, such as whirlwinds or waterspouts in regions where these are 

 extremely rare, have been advanced as explanations. All that is 

 necessary to explain this phenomenon is an exceptionally large survival 

 of tadpoles to metamorphosis. The original population of tadpoles is 

 sufficient to give rise to astonishing numbers, and the reason why this 

 is not more often seen is that the death rate of the tadpoles is usually 

 too high. The phenomenon itself is not important — we should very 



67 



