90 BEHAVIOR OF PIGEONS. 



normally happen, so that recuperation may end in about a week's time, when incubation 

 will stop and a new cycle begin, leading to the production of a second set of eggs in the same 

 nest. This has happened several times with the crested pigeon of Australia (Ocyphaps 

 lophotes) . 



Schneider 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 contrary, 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 on only secondarily and as an adaptation in correla- 

 tion 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 incubation 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 connections in the indi- 

 vidual, and independently of its developmental 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. 



(1) 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. 



(2) The primary roots of instincts reach back to the constitutional properties of proto- 

 plasm, and their evolution runs, in general, parallel with organogeny. As the genesis of 

 organs takes its departure from the elementary structure of protoplasm, so does the genesis 

 of instincts proceed from the fundamental functions of protoplasm. Primordial organs and 

 instincts are alike few in number and generally persistent. As an instinct may sometimes 

 run through a whole group of organisms with little or no modification, so may an organ 

 sometimes be carried on through one or more phyla without undergoing much change. 

 The dermal sensillse of annelids and aquatic vertebrates are an example. 



(3) Remembering that structural bases are relatively few and permanent as compared 

 with external morphological characters, we can readily understand why, for example, 

 500 different species of wild pigeons should all have a few common undiff erentiated instincts, 

 such as drinking without raising the head, the cock's time of incubating from about 10 a. m. 

 to about 4 p. m., etc. 



(4) Although instincts, like corporeal structures, may be said to have a phylogeny, 

 their manifestation depends upon differentiated organs. We could not, therefore, expect 

 to see phyletic stages repeated in direct ontogenetic development, as are the more funda- 

 mental morphological features, according to the biogenetic law. The main reliance in 

 getting at the phyletic history must be comparative study. 



(5) Instinct precedes intelligence both in ontogeny and phylogeny, and it has furnished 

 all the structural foundations employed by intelligence. In social development also instinct 

 predominates in the earlier, intelligence in the later stages. 



(6) Since instinct supplied at least the earlier rudiments of brain and nerve, since 

 instinct and mind work with the same mechanisms and in the same channels, and since 



1 Der Thierische Wille, pp. 282, 283, as cited in Professor James's Psychology, p. 388. 



