vi INSTINCT 73 



and functions are everyday matters too familiar to strike 

 us. The observant naturalist can carry this correspondence 

 further into detail, as when Dr. A. R. Wallace shows that 

 the absence of nests among the Megapodidae is correlated 

 with the large size of their eggs. This involves an 

 interval of ten or twelve days between the maturation of 

 each egg, and makes it impossible that all should be 

 hatched together. 1 But to complete the account of the 

 relation between structure and function, we should require 

 a knowledge of the molecular structure of the nervous 

 system of which we are as yet only at the beginning. 

 The reason why the bird uses its wings, or the tiger its 

 claws, is not merely that they possess wings and claws, but 

 that the muscles of wings and claws are connected through 

 a ramification of nerve fibres with their sense organs. If 

 we could trace out these ramifications in detail, we should 

 be able to specify the actual hereditary structures on 

 which the flying of the bird or the crouch and spring of 

 the tiger depend. We are only on the threshold of the 

 investigations necessary for such a purpose. 2 But we have 

 no reason to doubt that as in general so in detail we should 

 find a close correspondence between inherited structure and 

 inherited mode of action, which would justify us in 

 regarding the latter as the response made by the former to 

 accustomed stimulus. 



4. Treating instinct, then, as the response of inherited 

 structure to stimulus, comparative psychology at one time 

 inclined to regard it as closely related to reflex action. 

 The smell of putrid meat attracts the gravid carrion fly. 

 That is, it sets up motions of the wings which bring the 

 fly to it, and the fly having arrived, the smell and the 

 contact combined stimulate the functions of oviposition. 



1 Malay Arcihpelago, Vol. I. p. 418. 



2 Here and there by good fortune we come upon a progressive series 

 showing the stages by which evolution may have gone forward. " The 

 Synagris are a genus of Eumenidae ... 5. calida . . . stocks the cells 

 with caterpillars, lays an egg in each, seals the cells and takes no more 

 notice of them. S. sicheliana . . . places in each (cell) enough cater- 

 pillars to last the larva a little more than one day, and replenishes the 

 store daily." 6". cornuta completes one cell, lays an egg in it, does not 

 store it but feeds the hatched larva till it is full-grown, when the wasp 

 seals the cell and constructs another." E. Roubaud as summarised 

 J.A.B. 1912, p. 391. 



