522 S. O. MAST 



The results taken as a whole consequently support the con- 

 tention that the relation between wave-length and stimulation 

 in the blowfly larvae is more nearly like that in Chlamydomonas 

 than like that in any of the other organisms studied but that th,e 

 longer waves are somewhat more effective in the former than in 

 the latter (table 15). 



Gross ('13) made a very thorough study of the blowfly larva 

 with reference to the relative stimulating efficiency of four differ- 

 ent spectral colors, blue (420-480 mm), green (490-550 ij.ii), yel- 

 low (570-620 ixiji) and red (630-650 mm) • In this study he forced 

 the larvae to enter the side of a field of light consisting of two 

 horizontal beams with rays opposite in direction and different in 

 color but equal in energy. Under these conditions the beam 

 from which they turn is, of course, .the more efficient of the two 

 in which they are exposed. By thus testing successively various 

 combinations. Gross found the order of efficiency in the four colors 

 tested to be green, blue, yellow, red. These results are in full 

 harmony with those presented above, as can be clearly seen by 

 referring to table 15 and figure 4. 



DISCUSSION 



The results obtained show clearly that the reactions in all of 

 the species studied are dependent upon wave-length, certain colors 

 are much more efficient as stimulating agents than others, but 

 they are not wholly dependent upon wave-length, for while there 

 is clearly a region of maximum stimulating efficiency in the spec- 

 trum, stimulation is not confined to this region and the stimu- 

 lating effect of the wave-lengths on either side of it can be made 

 greater by simply increasing their intensity. There is conse- 

 quently no evidence in the results obtained indicating the pres- 

 ence of color-vision in any of the forms studied, for it is the 

 absence of any such relation between reactions and intensity 

 that constitutes the chief objective characteristic of color- 

 vision. 



Moreover, the fact that there is no variation in the distribution 

 of stimulating efficiency in the spectrum dependent upon differ- 

 ent physiological states, it being the same in specimens, e. g., 



