236 BIOLOGICAL LECTURES. 



For convenience let us call the anterior half of the worm a 

 and the posterior half b. Now if a be cut in two in the mid- 

 dle, the anterior piece a\ elongates and begins to crawl, while 

 the posterior piece a^ acts like b ; i.e., executes jerking and 

 squirming motions. Thus far in the experiment each piece 

 that began the progressive movements immediately after the 

 injury was the anterior piece, containing the so-called brain. 

 Now if we cut in two the posterior half b, we get just the same 

 kind of reactions as in case a — namely, the anterior part b\ 

 elongates and begins progressive motion, while the posterior 

 piece bz acts as Uz, carrying out a series of jerking and squirm- 

 ing motions. We observe, then, that each time after the halving, 

 the anterior piece elongates without any irregular muscular 

 contractions and begins to crawl forwards, while the posterior 

 piece always executes the same kind of squirming motions. 



The experiment may be carried still further, and each of the 

 four pieces cut in two. In each case the posterior half (one- 

 eighth of the whole worm) immediately begins the jerking and 

 squirming motions, while the corresponding anterior half elon- 

 gates and, if not too short, begins to crawl. Indeed, if small 

 visforous worms be used, the characteristic reactions of the two 

 halves may be observed in pieces that are only about five 

 millimeters in length. 



As to the significance of the reactions of the lower animals, 

 there are two opposite views. Those supporting the one view 

 assume that the reactions to external stimuli are the outward 

 expression of psychical processes resulting therefrom. The 

 larvae of crustaceans, for example, may prefer blue light to 

 red, if there be opportunity for choice. " The flesh-fly, Mnsca 

 carnaria, deposits its eggs in the flowers of the carrion plant, 

 the smell of which resembles that of putrid meat, and so 

 deceives (!) the fly." ^ Again, according to the same way of 

 reasoning, the moth flies into the flame, prompted by curiosity 

 to get acquainted with the strange object. 



The supporters of this view ignore the difficulty that con- 

 fronts them — namely, that the only means of determining 

 the presence of consciousness in the lower animals are the 



1 Romanes, Mental Evolution in Animals, p. 167. 



