362 OVIPOSITION AND HABITS OF CERTAIN BATRACHIANS, 



a longer or shorter period. This interesting state of things — in 

 correspondence with which the creeks and ponds, except of course 

 during such unfavourable seasons as we have recently had when 

 these have had little or no chance of becoming established, may- 

 be found more or less teeming with tadpoles throughout the 

 year — is attributable to at least three or four causes : — (1) 

 Dependence of the oviposition on the rainfall, itself irregular; 



(2) Seasonal differences in the breeding times of different species ; 



(3) The prolongation of the breeding seasons owing to the fact that 

 all the females of a given species may be far from simultaneously 

 ready to spawn at a given time ; and possibly (4) some species 

 may breed normally more than once during the year. The mild 

 climate is perhaps also a factor which should not be entirely over- 

 looked. 



The rainfall is a most important factor in regulating the dates 

 of oviposition, inasmuch as a heavy downpour of rain is often 

 necessary to release the frogs from their aestivation, and in many 

 cases to provide the water-supply in which the spawn is to be 

 deposited. A heavy downpour of rain succeeding a period of dry 

 weather will set some frogs spawning at any time of the year ; 

 and on the other hand, in whatever month the frogs spawn, as a 

 general rule they do so as soon as the weather clears up after 

 rain. In the case of the swamp frogs, if, as in very favourable 

 years, the ponds are full when the frogs are ready to spawn, no 

 doubt they do so ; but in very dry seasons they are in the same 

 plight as the less aquatic species. 



In England Rana temporaria spawns with considerable regu- 

 larity at the end of February or beginning of March, the spawning 

 lasting about a fortnight ; while on the continent two varieties of 

 R. escidenta spawn within a fortnight of each uther, a fact which 

 is held to be of importance as indicating that they are distinct 

 races, and in maintaining their distinctness.* Similar regularity 

 has been noted in the case of American frogs, f With our frogs 

 there is much irregularity, and the ovipositing periods, instead of 



* P.Z.S. 1885, p. 670. 

 t Packard's *' Zoology" pp. 484-487, 



