BRAIN PHYSIOLOGY OF WORMS 



347 



FIG. 98 



Schrader has found that a frog is possessed of an irresistible 

 impulse to move after losing this center. 1 



The simplest facts of comparative physiology show more- 

 over that the power of progressive movement is possessed 

 also by such organisms which have no brain whatever, i. e., 

 the swarm spores of Algse. It is, in 

 my opinion, not the problem of physi- 

 ology to find a definition for an organ 

 but to discover the functions of a given 

 organ. 



From this standpoint I wish to make 

 in the following pages some contribu- 

 tions to the brain physiology of worms. 

 I understand in this paper by the term 

 brain, as is customary, the ganglia lying 

 at the oral end of these animals. Brain 

 physiology has shown that for the higher animals the biologi- 

 cal character of a species, that is, the sum total of those 

 reactions of a species which are determined by the external 

 surroundings, depends chiefly upon the brain. I was espe- 

 cially interested in determining whether the rudimentary 

 brain of such low animals as the worms has a similar signifi- 

 cance. The experiments which I wish to report have been 

 made at long intervals, some in Naples in 1889, some in 

 Woods Hole in 1893. 



II 



I. EXPERIMENTS ON THYSANOZOON BROCCHII 



1. Thysanozoon is an elliptically shaped marine Planarian 

 (Fig. 98, according to Lang), which is from one to three cm. 

 long, and almost as broad. The brain g of the animal, an 

 unpaired organ, is situated at the anterior extremity of the 

 body, which latter can be recognized without difficulty by 



i SCHEADER, Pflugers Archiv, Vol. XLI. 



