328 BIOLOGICAL LECTURES. 



This has happened several times with the crested pigeon of 

 Australia (OcypJiaps lophotes). 



Schneider 1 says : " The impulse to sit arises, as a rule, when 

 a bird sees a certain number of eggs in her nest." Although 

 recognizing a bodily disposition as present in some cases, sitting 

 is regarded as a pure perception impulse. I hold, on the con- 

 trary, that the bodily disposition is the universal and essential 

 element, and that sight of the eggs has nothing to do primarily 

 with sitting. It comes in only secondarily and as an adapta- 

 tion in correlation with the inability in some species to rear 

 more than one or two broods in a season. In such species the 

 advantage would lie with birds beginning to incubate with a 

 full nest. 



The suggestions here offered on the origin of the incubation 

 instinct, incomplete and doubtful as they may appear, may 

 suffice to indicate roughly the general direction in which we 

 are to look for light on the genesis of instincts. The incuba- 

 tion instinct, as we now find it perfected in birds, is a nicely 

 timed and adjusted part of a periodical sequence of acts. If 

 we try to explain it without reference to its physiological con- 

 nections in the individual, and independently of its develop- 

 mental phases in animals below birds, we miss the more 

 interesting relations, and build on a purely conjectural chance 

 act that calls for a further and incredible concatenation of the 

 right acts at the right time and place, and is not even then 

 completed until its perpetuation is secured by a miracle of 

 transmission. 



A FEW GENERAL STATEMENTS. 



i. Instinct and structure are to be studied from the common 

 standpoint of phyletic descent, and that not the less because 

 we may seldom, if ever, be able to trace the whole development 

 of an instinct. Instincts are evolved rather than involved 

 (stereotyped by repetition and transmission), and the key to 

 their genetic history is to be sought in their more general 

 rather than in their later and incidental uses. 



1 Der Thierische Wille, pp. 282, 283. As cited in Professor James's Psychol- 

 ogy, P- 388. 



