110 TBOPISMS 



efficiency of the two beams was considered equal. Mast's 

 results, w T hich are given in Table X, agree with those of 

 Loeb and Wasteneys. 



The error which Hess makes is of epistemological in- 

 terest inasmuch as it shows the danger of false analog}". 

 The real analogy for heliotropic reactions are forced 

 movements and other tropisms, e.g., galvanotropism or 

 geotropism. Since forced movements (e.g., in Meniere's 

 disease) and galvanotropic reactions caused by a constant 

 current through our head are not determined or accom- 

 panied by special sensations, the same may be true in 

 regard to heliotropic reactions. This is not an idle 

 assumption, since we know that the contraction of the 

 iris of our eye under the influence of light is not accom- 

 panied by any sensation of brightness or color and such 

 contractions occur also under the influence of light when 

 the iris is excised. Hess ignores not only this analogy, 

 but the whole existence of forced movements and of other 

 tropisms, and he uses the color and light sensations of 

 human beings, who are not heliotropic, to explain helio- 

 tropism in animals about whose sensations we know noth- 

 ing. He fails to see that by this false analogy he dodges 

 the real problem of heliotropism, namely, why the tension 

 of symmetrical muscles changes upon one-sided illumina- 

 tion of an animal. For the explanation of this problem, 

 we find assistance in the field of forced movements and of 

 galvanotropism and of geotropism, but not in the behavior 

 of totally color blind human individuals who show no 

 trace of heliotropism. 



The adoption of the false analogy between visual sen- 

 sations and heliotropism makes it impossible for Hess 

 to admit that bees should be heliotropic and at the same 

 time be able to discriminate between blue and gray ; while 



