272 



GERTRUDE MAREAN WHITE. 



relative energy value of 1176 (Table I.), and this number was 

 divided by the relative energy value for each of the other filters. 

 The resulting quotient in the case of each filter was then multiplied 

 by the value for the relative stimulating effect of the light for that 

 filter, thus giving values for the relative stimulating effect of 

 light of equal energy content. 



TABLE II. 



RELATIVE STIMULATION OF LIGHT TRANSMITTED BY DIFFERENT FILTERS. 



The results obtained (Table II. and Fig. 4) show that for both 

 the shrimp and squid larvae the maximum stimulation is in the 

 blue-green (470 ^-510 MM), and that yellow-green (520 MM~ 

 550 JUM). yellow (550MM-590MM), and blue (420 MM~47O MM) are 

 less stimulating. All these wavelengths are more stimulating 

 for squid than for shrimp larvae, particularly the blue-green and 

 blue which are more than twice as effective. The rays beyond 

 620 MM do not seem to effect squid larvae at all, while shrimp 

 larvae, though not so powerfully stimulated, show some reaction. 



Since both shrimp and squid larvae possess eyes, it is reasonable 

 to suppose that their reactions are due, to a large extent at least, 

 to the nature of the photosensitive substances present in the eyes. 

 Whether this is associated at all with the fact that the shrimp eye 

 is compound while the squid has camera eyes would be interesting 

 to learn. 



Mast (1917) found from the study of fifteen species of various 

 types that stimulation by light depended upon the wave-length. 

 The distribution of stimulating efficiency in the spectrum 

 differed in various forms without any apparent relation as to 

 whether they were closely related species or not. It may be 



