THE SUMMIT OF THE YEARS 



can at any time be made to grow wings by simply 

 lowering the temperature, or by letting the plant 

 upon which they are feeding dry out. The egg-laying 

 mechanism of the blow-fly is set going by certain 

 volatile substances contained in its meat, and this 

 he calls chemotropism. 



Still, one would like to know how this particular 

 kind of machinery came to be developed in the blow- 

 fly. The terms " reflexes" and " tropisms" do not 

 give a plummet-line long enough to sound all the 

 depths of animal behavior. With them one may 

 measure very well the conduct of the lower organ- 

 isms, such as radiates, articulates, mollusks. The 

 lives of these creatures are mainly a series of reflexes 

 or tropisms. We could not correctly speak of the 

 psychology of a clam, an oyster, or a worm, because 

 they have no psychic life; but their tropisms or auto- 

 matic responses to stimuli are interesting to study. 

 These lower forms have no instincts, properly so 

 called. Not until we get higher in the scale of life, 

 and reach animals that have associative memory, 

 do we reach the region of psychics, and find that 

 complex behavior which we designate as instinctive, 

 and which results as much from inborn impulses as 

 from outward stimulation. 



Loeb is of the opinion that all so-called instincts 

 will ultimately be explained on purely physiological 

 principles, that is, on the physical and chemical quali- 

 ties of protoplasm. When this is done, the difference 

 170 



