The sensitive area which forms the basis of 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 organism follows the segment. It has been customary among physiologists to speak of reflexes in such cases. Thus, _e. g._, 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 determined by specific substances which also determine the tropistic reaction (as well as phenomena of organ formation, although this latter phenomenon has nothing to do with the subject of instincts); and the excellent work of Cannon[246] has shown the rôle of adrenalin in the expression of fear. It is, therefore, both unwarranted and unnecessary to state that hypothetical emotions determine the tropistic reactions. [246] Cannon, W. B., _Bodily Changes in Pain, Hunger, Fear, and Rage_, New York, 1915. CHAPTER XI THE INFLUENCE OF ENVIRONMENT