388 WAVE-LENGTH AND PHOTOSENSORY PROCESS 



Wasteneys, 1916; Mast, 1917). Although for many animals this 

 point lies in the yellow-green, and for many plants in the blue-green, 

 there is an increasing number of organisms which do not conform to 

 this classification. Mya arenaria clearly belongs in this non-conform- 

 ing category, because it is an animal for which the maximum effective- 

 ness is in the blue-green. 



The particular significance of the above attempts at classification is 

 due to Hess (1910). As the result of experiments with a number of 

 animals, Hess has come to the conclusion that "the curves of the rela- 

 tive stimulating values of different homogeneous lights coincide, 

 approximately or exactly, with the luminosity curve of the totally 

 color blind human eye" (Hess, 1910, p. 362). From which he pro- 

 ceeds to draw certain conclusions with regard to the nature of the 

 responses of animals to light. Loeb and Wasteneys (1916) have 

 shown that these conclusions not only fail to agree with the facts of 

 other investigators, but also that the process of arriving at them in- 

 volves a decided logical fallacy. If after this any additional evidence 

 were needed, the results with Mya certainly show that Hess' original 

 statement is not generally true. The curve of effectiveness of the 

 spectrum for Mya possesses nothing in common with the luminosity 

 curve for the color blind or the dark-adapted human eye. 



It may be added that Hess' method of experimentation is open to 

 criticisms which invalidate his conclusions. Working with certain 

 clams whose photic sensitivity is similar to that of Mya, he employs 

 criteria of the effectiveness of light which cannot be considered quan- 

 titative. He notes the length of the extended siphon, or the extent 

 of its retraction as the animal is moved along the projected spectrum. 

 My experience with Mya has been that these are variable character- 

 istics, even when care is taken to insure uniformity otherwise. In 

 Hess' experiments no values are given for the energy content of the 

 spectrum; no time is allowed for the recovery of an animal in the 

 dark between stimulations ; no measurements are made of the time of 

 exposure ; no record is made of the reaction time. In fact, few measure- 

 ments of any kind are given. Even the "curves" on which the com- 

 parison with the human eye rests fail to appear in the article (Hess, 

 1910). Thus, even if Hess' logic were correct, his experimental find- 

 ings are open to grave doubt; and the conclusions drawn from them 

 are therefore doubly invalid. 



