284 Animal Instincts and Tropisms 



is as a rule developed not in the whole organism but 

 only in certain segments of the body. Thus the eyes 

 are located in the head. But when the action of 

 one segment becomes overpowering the whole or- 

 ganism follows the segment. It has been customary 

 among physiologists to speak of reflexes in such cases. 

 Thus, e. g.j the arms of the male frog develop a powerful 

 positive stereotropism on their ventral surface during 

 the spawning season. It would avoid confusion to 

 realize that there is nothing gained in applying to this 

 tropism the meaningless term "reflex"; it is better to 

 call them tropisms since the organism as a whole is 

 involved. If necessary we might speak of segmental 

 tropisms. The act of seeking the female as well as 

 that of cohabitation are in many cases combinations 

 of chemotropism and stereotropism. The development 

 of these tropisms depends upon the presence of certain 

 specific substances in the body, a fact emphasized 

 already in the case of heliotropism. In case of the 

 development of the segmental stereotropism of the male 

 frog at the time of spawning it has been shown that it 

 depends on an internal secretion from the testes. 



It has been suggested by some authors that the 

 tropistic reactions are determined by some feeling or 

 emotion on the part of the organism. We have no 

 means of judging the emotions of lower animals (except 

 by "intuition''). The writer suggested in 1899 in his 

 book on brain physiology that emotions may be deter- 



