MALES ARRIVE UK TORE FEMALES 37 



the males must be the first to leave their winter 

 quarters. 



What is meant by the " migratory instinct "? 

 To speak of it as one of the instincts concerned 

 in reproduction is not enough. Reproduction 

 involves the actual discharge of the sexual 

 function, which involves the females ; but the 

 first visible manifestation of organic change in 

 the male is its desertion of the females. Yet 

 this is the behaviour which is referred to as the 

 " migratory instinct," and which comes into play, 

 according to this theory, because the bird has 

 reached sexual maturity. Manifestly we must 

 have some clear understanding as to what these 

 terms represent. That organic changes deter- 

 mine the functioning of certain definite instincts 

 at certain specified times there can be no doubt ; 

 that these changes may occur at a somewhat 

 earlier date in the male than in the female is 

 more than probable, but that this explains the 

 behaviour in question I do not believe. One 

 wants to know why the changes should occur 

 earlier in the male, what disposition it is which 

 first comes into functional activity, and to what 

 such disposition is related. 



It may, however, be urged that, after all, 

 this apparent eagerness to reach the breeding 

 grounds is but a modification of hereditary pro- 

 cedure under the guiding hand of experience. 

 What more likely result would follow from the 

 enjoyment associated with previous success in 

 the attainment of reproduction than a craving to 

 repeat the experience ? What stronger incentive 



