The Sense of Sight in Spiders 279 



splendid experiments of Mr. and Mrs. Peckham on the jumping 

 spiders (Attidae), during the mating period, have clearly demon- 

 strated that the sexes recognize each other by the use of their eyes 

 alone, the male remaining unaware of the presence of a female, 

 nor will he perform the peculiar, characteristic love dance, if his 

 eyes are covered with paint. But is the sense of sight in spiders 

 as sharp as we should be led to expect by comparison with that 

 of birds of prey ? This question has not yet been answered with 

 sufficient certainty owing to the difficulty of experimenting. 

 Plateau came to an entirely negative conclusion, asserting that 

 spiders possess an indistinct and very poor vision, being unable 

 to discern objects beyond a distance of from 8 to 10 cm. Forel 

 was of the same opinion, while the more ingenious experiments of 

 the Peckhams leave no doubt that the males of the Attids recog- 

 nize their females at a distance of about 30 cm. and moreover 

 that they distinguish colors. But whether spiders can see beyond 

 this distance and how sharp their vision is, the experiments of 

 the Peckhams also, leave unanswered. In fact it would be impos- 

 sible to answer this question merely by observing the behavior 

 of spiders during an experiment or in nature. A close anatomico- 

 physiological study is required and only by combining the experi- 

 ment on the living specimen with its after examination may one 

 reach a satisfactory answer. This answer I hope to have given 

 in the present research. 



Keeping in mind all that has been said in the preceding pages, 

 we may conclude that the study of the eyes of spiders and of their 

 sense of sight, as examples of adaptation of the first kind, pos- 

 sesses several advantages as well as certain disadvantages and 

 these we have next to consider. The advantages are: 



1 That the sense of sight is beyond any doubt the only sense 

 that guides hunting spiders on their hunting excursions and in 

 finding the females during the mating period. 



2 That the eyes of spiders are organs which are for each species 

 definite in number and position on the cephalothorax. 



3 That the sense of sight is a sense common to the great 

 majority of lower and higher animals and that some analogizing 

 is therefore not only admissible but may be of great value. 



