Brain PHystoLoGcy or Worms 347 
Schrader has found that a frog is possessed of an irresistible 
impulse to move after losing this center.’ 
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, ¢. e., 
the swarm spores of Alge. 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 BIG 28 
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 
1SCHRADER, Pfliigers Archiv, Vol. XLI. 
Digitized by Microsoft® 
