Preli?7iinary Definitions and Illustrations. 13 



Many of these activities are so familiar to the obser- 

 vant naturalist, constituting as they do the normal life- 

 habits of the animals which exhibit them, that they are apt 

 to suffer the common fate of the familiar, and receive less 

 notice and less attention than the unusual and unfamiliar. 

 That an insect should exhibit one set of activities as a 

 larva or caterpillar, and a totally different set of activities 

 as an imago or perfect insect, seems quite natural, and 

 what we should expect. But the naturalist, who is some- 

 thing more than a collector, sees in these activities 

 problems not less difficult of solution than are the problems 

 of structure with which they are associated. And, in any 

 consideration of instinct, these familiar activities which 

 are performed under the ordinary circumstances of normal 

 life must not be allowed to fall into the background. They 

 form the largest, if not the most conspicuous, group of 

 instinctive activities. 



But there are other instinctive activities which are 

 performed seldom or only once, and these are in all cases 

 of vital importance to the continuance of the race. Of the 

 many drones which follow the queen-bee in her nuptial 

 flight, one only is successful in mating with her, and that 

 but once in his life. And yet, were the sexual instinct 

 of drones to lapse, even for a single year, the race would 

 be decimated ; and were it to lapse altogether for but a 

 few years, the race would become extinct. The instinct is 

 essential to the preservation and continuance of the race. 

 And many of these instinctive activities thus but seldom 

 performed are adaptive with a nicety which is a continual 

 source of our wonder and admiration. Of such exquisite 

 adaptation we may take, for example, the instinctive 

 activities* of the Yucca moth (Pronuba yuccasella). 



* Described in Kernels "Natural History of Plants," translated and 

 edited by Prof. Oliver, vol. ii. p. 156. 



