upon the proportion of the sexes produced by Canaries. 205 
mature during each breeding season, these ova are subject to 
selective action, an action with which the quantity or quality of 
the nutriment supplied has much to do. 
Here I suggest that the factors which mainly governed the 
results shown for these two aviaries were, for G, a temperature 
and aspect which conduced to early breeding and the early 
maturation of ova which had not received specially rich nutrition. 
The generative functions of these birds was in fact “ forced ” with- 
out being richly fed and they produced males in great excess. 
iV’s birds, on the other hand, were kept back, they both nested 
later and moulted later than G’s birds, their generative functions 
were not stimulated, the ova matured more slowly and were at the 
same time more Highly fed, and these birds produced a marked 
excess of females. 
A similar result, obtained by forcing and retarding develop- 
ment in plants, is recorded by Meehan and by Bordage, whose 
works are noted in my paper on Dogs referred to above. 
As a rule in nature the climatic forces which stimulate the 
activity of the generative functions are also associated with a 
plentiful supply of food, the conditions which excite the one 
ensure the supply of the other. Among domesticated animals 
living in the open air, on the other hand, any forcing of the 
breeding time is brought about by special feeding. In neither 
case are the results obtained comparable to those we have now 
before us, where both the quality and the quantity of the food 
supplied is regulated entirely independently of the other causes 
which stimulate the activity of the generative system. 
It is to this peculiar combination I attribute the regularity of 
the remarkable differences shown in these two aviaries. 
