THE ENVIRONMENT AND REPRODUCTION 29 



failure is obscure because about the same time Marshall 

 and Bowdeni33 ^[({ cause a stoppage of spring breeding 

 by means of light restriction, and they also quoted the 

 ca^e of a blind ferret (with cataract) which never came on 

 heat although.fit fed well and remained apparently 

 healthy for two years. Bissonnette,^^ by light restriction, 

 also prevented the spring breeding of ferrets. 



Other mammals which have responded by sexual 

 development to increasing light are the hedgehog,^ 

 and the raccoon.^^ 



The lower vertebrates have not yet been studied so 

 intensively, but similar results have been obtained in 

 some cases. Among reptiles increased spermatogenic 

 activity following artificial illumination has been 

 reported in the case of the lizard Anolis carolinensis^^ and 

 of the turtle Pseudemys elegans. ^^ 



However, no amphibian has yet been proved to be 

 sensitive to an increase in light alone, and, as might be 

 expected, the importance of temperature is greater in 

 such cold blooded animals, as it also is among the fishes. 

 In species such as the edible frog^* and the killifish^® 

 temperature is of critical importance, and the effect of 

 light is negligible. However, in the case of the little fresh 

 water minnow, it has been found that long days of arti- 

 ficial light in late autumn and winter can induce com- 

 plete maturation of both testes and ovaries.*' This result 

 is only obtained if the water temperature exceeds about 

 10° C., but a high temperature alone is ineffective. 

 Such joint action of extra light and high temperature is 

 also necessary for maturation in the four-spined stickle- 

 back. "9 



The studies which have been made on the lower 

 vertebrates are still too few to enable an overall picture 

 to be drawn. In particular it would be interesting to 

 obtain information regarding the reproductive cycles of 

 a variety of marine species living in temperate regions. 



