HEAIN PHYSIOLO<M OK \Voims 



:-H7 



Schrader has found thai 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 1 train whatever, /. r., 

 the swarm spores of Algae. It is, in 

 my opinion, not the problem of plnsi- 

 ology lo rind 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 FIG - 98 



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 wisli to report have been 

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

 Woods Hole in 1893. 



II 



I. EXPERIMENTS OX THYSANOZOON BROCCHII 



1. Thysanozoon is an elliptically shaped marine Planarian 

 (Fig. 9S, according to Lang), which is from one to three cm. 

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

 unpaired organ, is sit nated at the /interior extremity of the 

 body, which latter can be recognized without difficulty by 



i Srm: \ipi.i:. I'llni/crs Arcliir. Vol. XLI. 



