The Sense of Sight m Spiders 277 



A caterpillar that is able to construct a better protected cocoon 

 than its fellows, an animal that can run faster from danger, a 

 bird of prey that distinguishes its victim at a greater distance, all 

 these will evince their superiority over other individuals of the 

 same species upon the first occasion. Here, then, opportunity is 

 given for a more rapid accumulation of characters and an acceler- 

 ated selection. Several years ago I studied, together with Dr. 

 von Guaita, although with a different object in view, the stridu- 

 lating organs of Orthoptera. These organs are undoubtedly not 

 of a protective character as the insects in question are safer when 

 silent. This is sufficiently shown by the fact that they stop their 

 cry instantly upon the approach of danger. The origin of the 

 stridulating organs has therefore to be sought in some advantage 

 which they may afford the sexes during the mating period. That 

 they are a rather late acquisition is evidenced by their late appear- 

 ance, only with the last moulting, while the rapidity of selection 

 which in this case must still have been retarded by the danger 

 arising from their possession, is apparent from the complete 

 absence of any traces of similar organs previous to the last moult- 

 ing. The great variability in the number of teeth on the chord or 

 bow of the stridulating apparatus, which permits of difference of 

 pitch in the tones produced by friction, the fact, with other words, 

 that the stridulating organs are in respect to their details, not 

 absolutely fixed structures, seems to be due to this antagonism 

 between the advantage afforded by the organs in the relation of 

 the sexes toward each other and their disadvantage in respect to 

 diminished safety from the aggression of enemies. But how is it 

 with organs in which the advantage arising from their perfecting 

 will be immediately exploited to its fullest extent by the animal 

 possessing them ^ With this question before me I commenced 

 my research on the sense of sight in spiders. The results of this 

 research which now extends over more than a year, I bring in this 

 paper. 



Two factors in the life of spiders have left a deep impres- 

 sion on their organization, the first, that they subsist exclusively 

 by means of prey and the second, that the external sexual organs, 



