THE ENVIRONMENT AND REPRODUCTION 35 



atozoa. In Baker's words, *No animal living in a strongly 

 seasonal climate could have a more sharply defined 

 breeding season. This seems all the more extraordinary 

 when it is remembered that this little bat hangs through- 

 out the pepod of daylight, till about ten minutes before 

 sunset, in a dark and almost thermostatic cave.' 



Of the birds, the golden whistler also has a sharply 

 defined breeding season with most of the egg-laying 

 crowded into one month, and Baker was therefore 

 driven to the conclusion that the various vertebrates 

 studied are at least as seasonal in their reproductive 

 habits as are those in temperate climates. 



The second question then remained to be answered, 

 namely what regularly varying factors in the environment 

 are responsible for the timing of these seasons? To this 

 it is not yet possible to give any answer. It was noted that 

 the reptile Emoia bred most actively in November and 

 December when the days were at their longest, while the 

 golden whistler behaved in an exactly opposite manner. 

 Thus these two animals may conceivably be influenced 

 by the slight variations in daylength. To Miniopterus, 

 which only leaves its dark cave at nightfall, the duration 

 of daylight would seem to be a matter of little moment. 



One way in which it has been suggested that light 

 might influence tropical animals is through its quality or 

 its intensity. In the New Hebrides there is, for example, 

 far less ultra-violet light in some months such as June 

 than in others such as December, and perhaps an 

 animal could be conditioned to react to this fluctuation. 

 Again in many other parts of the tropics there are 

 alternating wet and dry seasons with a lower intensity of 

 light at those times when the days are cloudy. 



Partly no doubt because of the war, little more has 

 been done in analysing this problem of tropical breeding 

 seasons. However, Marshall 129 has recently published 

 results which show that the fruit bat Pteropus giganteus, 

 living in the stable climate of Ceylon, has a single sharply 

 defined breeding season in December. In this it follows 



