The Sense of Sight in Spiders 307 



the most intricate questions proves to be its weak point and it no 

 longer suffices. How indeed, for example, can we accept the 

 explanation given for the existence of the black shield at the base 

 of the bill of the white swan, as a protection against the blinding 

 light reflected from the surface of the water, when another water 

 bird of the same fauna — Fulica atra — has black plumage and a 

 snow white shield ? The difficulty is gotten round by explaining 

 the latter case from the point of view of sexual selection or in 

 some other way. The number of similar cases could be multi- 

 plied indefinitely. It is clear that if we desire to hold to the 

 principle it will be necessary to show step by step the progress 

 of adaptation in indisputable cases. Of this nature are variations 

 of which the animal itself can immediately make use to its own 

 advantage over its rivals. While the origin of the variations 

 themselves is a field for other research I hope to have shown in 

 the present study of the sense of sight in spiders, the probable 

 course of adaptation in the survival of the fittest. 



Short Hills, New Jersey 

 August II, 1907 



