STUDIES IN ADAPTATION 



I THE SENSE OF SIGHT IN SPIDERS 



BY 



ALEXANDER PETRUNKEVITCH, Ph.D. 

 With Six Plates 



Whether the organization of an animal is the result of contin- 

 uous adaptation to the conditions of life, or whether the animal 

 adapts itself as best it may to the use of organs in the possession 

 of which it has been put by nature, an impartial observer sees 

 everywhere the remarkable balance between structure and function. 

 The few apparent incongruities which we meet with in all groups 

 of the animal and vegetal kingdoms, only serve to confirm the 

 rule, since they are due largely to our lack of knowledge of the 

 conditions under which such organs exist to their best advantage 

 or of the role which they played in the phylogenetic development 

 of the species. But however this may be, we should expect to 

 find, and there surely must be a marked difference between the 

 origin of organs by means of which the animal communicates 

 actively w^ith the surrounding world and that of such organs or 

 structures as lie entirely outside of the personal activity or con- 

 trol of the animal. It is very probable that many, perhaps the 

 majority of arthropods are entirely unaware of the presence on 

 their bodies of so-called decorative structures, designs or colors 

 and whether a male possessing a slight variation in such a 

 structure, design or color, will or will not be preferred by a 

 female, is to my mind entirely a matter of chance. In this con- 

 nection I can only confirm the observation of earlier naturalists 

 that females often choose defective males in the presence of 

 other in every respect perfect ones. I have caught in Europe a 

 pair of large beetles (Prionus coriarius), in coitu in the presence 

 of two other perfect males, when the male in question had 



The Journal of Experimental Zoology, vol. v, no. 2. 



