38 VERTEBRATE REPRODUCTIVE CYCLES 



The habit is common among birds in tropical Africa 

 and in India. It is particularly striking in Ceylon where 

 the north-east monsoon affects one side of the island at 

 one time of the year, while the south-west monsoon 

 affects the other side at quite a different time.i^' It has 

 also been suggested that the breeding of the wood 

 swallow of Western Australia is dependent on the rains 

 since it breeds either in February and March, or in 

 June and July, or at both times, according to whether 

 rain falls, i^ 



In the lower vertebrates similar conditions are known 

 to prevail in many species. Among reptiles it has been 

 noted for snakes and lizards in Oklahoma,^^ while 

 among amphibians, as might be expected, the habit of 

 relating breeding to rain is very widespread. The North 

 American toad, Scaphiopus bombifrons, spawns at the 

 first heavy rain after the middle of spring, and in a season 

 with little rain breeding may be delayed until the end of 

 the summer.io Rain also determines the breeding time 

 of the American toad Bufo cognatus.^^^ An extreme con- 

 dition is perhaps reached in the Australian desert where 

 after heavy rains frogs such as Chiroleptes platycephalus 

 swarm from the ground, where they have lain buried in 

 a state of aestivation, and spawn almost immediately. ^^ 

 For fishes there appear to be no data, but it seems 

 probable that the lung fishes, which sometimes also 

 aestivate, may react in the same way as do these am- 

 phibians. 



No experimental work has yet been done on this 

 problem, and it is not possible even to suggest how the 

 rain may achieve its effect. Indeed it is not even possible 

 to say whether the imxportant factor is the rain itself, or 

 as suggested by Baker i<^ the degree of saturation defi- 

 ciency of the air, or the psychological effect of the 

 existence of ponds or floods, or the increase in food 

 supply which accompanies the development of green 

 vegetation. In all probability the answer is not the same 

 in all species. 



