4 04 TEE POPULAR SCIENCE MONTHLY 



of protective coloration in connection with sexual selection, since it is 

 clear that the same objection, namely, the need of intelligence, may be 

 urged against the assumption of warning coloration. And warning 

 coloration is effective against some animals with distance receptors, but 

 not necessarily against animals without such sense organs. 



Visual and auditory mechanisms make their appearance well down 

 in the animal scale, and hence the possibility of reactions through these 

 mechanisms also arises rather low in the scale. The question then shifts 

 to the central nervous system, and we must inquire whether in any of 

 the lower forms, before the onset of intelligence, reactions to color are 

 possible. 



Since the work of Sumner 2 on the change of color pattern in 

 flounders when placed in an aquarium with a certain color pattern in 

 the bottom, we have known that reactions to color do occur under 

 certain conditions. There are, of course, certain limitations to the 

 process, and the mechanism of the response may still require investiga- 

 tion, but the response of the fish to visual impressions is undoubted, and 

 it would be a far cry to postulate intelligence in the process. If a 

 flounder responds to changes in the color pattern of the bottom of an 

 aquarium, it is apparently not a more serious offense to postulate a 

 response to a peculiar color pattern in another flounder. Other obser- 

 vations of the same kind on other animals lead to similar conclusions 

 with regard to response to color. In the terminology of the physiologist, 

 the response is a reflex process, involving an afferent or sensory impulse, 

 the mediation of the central nervous system, and some efferent or out- 

 going nervous channel to the pigment cells of the skin. The medieval 

 debate as to whether a reflex must always occur through the spinal cord, 

 or even through the palasencephalon 3 is quite beside the point. 



Another instance in which the appeal of color or odor is of impor- 

 tance is the attraction of bees and insects generally by flowers. The 

 debate on the color vision of bees is far from closed, but that color plays 

 some role will probably be admitted without prolonged argument. 

 Whether bees have a sense of smell may perhaps be an open question, 

 but that flowers attract bees seems clear. Both flower and insect visitor 

 often have developed extraordinary modifications of the primitive type 

 of structures so that neither insect nor flower can get along without the 

 other. The yucca plant and the Pronuba moth constitute a case in 

 point. Often but one species of insect can fertilize a particular flower, 

 and it may happen that an insect can successfully visit but one species 

 of flower. The question is not so much how the insect knows enough to 

 visit that particular flower, but what particular features of the flower 

 appeal to specific sense organs of the insect. 



2 Sumner, Journal of Experimental Zoology, 1911, X., pp. 409-479. 



s E&inger, Journal of Comparative Neurology, 1908, XVIII., pp. 437-457. 



