296 ENTOMOLOGY 



The selection theory of Darwin, Weismann, Morgan and others has 

 much in its favor. It regards reflex acts as primitive, as the raw material 

 from which natural selection, as the chief factor, has effected those com- 

 binations that are termed instincts. 



Instincts and Tropisms. We have already emphasized the fact 

 that an instinct is a reflex act or a combination of reflex acts. The same 

 fact may now be stated in these words: an instinct is a tropism or a 

 combination of tropisms. The more important of these tropisms have 

 been considered. Whenever possible it is better to discard the ambigu- 

 ous term instinct in favor of such more precise terms as photoiropism, 

 geotropism, etc.; though the term instinct remains useful as applied to an 

 action that is the resultant of several tropic responses. 



The modern student of instincts aims to resolve them into their 

 component reflexes and to determine as precisely as possible the influence 

 of each reflex component. Thanks to the labors of a great number of 

 skilled investigators, we are no longer satisfied to class an action as "in- 

 stinctive" and then dismiss it from thought; for now we are in a position 

 to analyze the action, and may hope to explain it eventually in terms of 

 the physical and chemical properties of protoplasm. 



3. INTELLIGENCE 



Though manifestly dominant, pure instinct fails to account for all 

 insect behavior. The ability of an insect to profit by experience indi- 

 cates some degree of intelligence. 



Take, for example, the precision with which bees or wasps find their 

 way back to the nest. This is no longer to be accounted for on the as- 

 sumption of a mysterious "sense of direction," for there is the best of 

 evidence for believing that it depends upon the recognition of surround- 

 ing objects. When leaving the nest for the first time, these insects make 

 "locality studies," which are often elaborate. Referring to Sphex 

 ickneumonea, the Peckhams write: "At last, the nest dug, she was ready 

 to go out and seek for her store of provision and now came a most thor- 

 ough and systematic study of the surroundings. The nests that had 

 been made and then deserted had been left without any circling. Evi- 

 dently she was conscious of the difference and meant, now, to take all 

 necessary precautions against losing her way. She flew in and out 

 among the plants first in narrow circles near the surface of the ground, 

 and now in wider and wider ones as she rose higher in the air, until at 

 last she took a straight line and disappeared in the distance. The dia- 

 gram [Fig. 295, A] gives a tracing of her first study preparatory to de- 



