No. 3.1 SEXUAL SELECTION IN SPIDERS. 147 



less is incapable of disproof.* Fortunately, in the case of 

 spiders the facts are quite different. The spider has four pairs 

 of legs, and all are equally available for display or locomotion, 

 and since all the movements are slow and on the ground they 

 are entirely open to observation and study, and we are thus in 

 a position to decide by facts whether their activity is simply an 

 outlet for superfluous energy, and therefore meaningless, or 

 whether there is a purpose in it. If the purpose of the antics 

 is only to let off energy, then we should expect one pair to be 

 flourished around quite as often as another, and that the pair 

 flourished should as frequently be one that was not ornamented 

 as one that was ; and, moreover, their movements ought not to 

 be of such a nature as to display the color or ornament more 

 frequently than the law of chance would explain. If the spider 

 almost always moves the ornamented legs, and in such a way, 

 too, as to bring out their beauty, it would seem to us, to say the 

 least, highly improbable that the dance of the spider was 

 merely a meaningless overflow of surplus energy. Such an 

 explanation leaves much that needs explanation. The facts 

 are, that the best foot is put forward ; and this is just what 

 Darwin's theory requires and explains. Under Mr. Wallace's 

 view the facts are inexplicable. The better to show that these 

 movements are not simply meaningless outlets of high vigor, 

 we illustrate the several positions by figures taken from nature 

 (Figs. 7-12). The figures would seem to prove that the 

 legs that are ornamented or contrasted in color are also the 

 legs that are usually flourished ; that where none of the legs 

 have special ornament, then all are used; or, as sometimes hap- 

 pens, when an unornamented leg is used the movements are of 

 such a character as to display some ornament that would other- 

 wise have been more or less hidden from the female. Mr. Wal- 

 lace, in his review f of Mr. Poulton's recent work on Color, 

 remarks, in this connection, that in the case of the black variety 

 of Astia vittata " there is not a particle of proof that the black 

 color was the cause of the selection rather than the ' superior ' 



* The absence of color on the flight feathers of hnmmlng-blrds, along with other 

 facts, shows that even In this class there is a good deal of evidence or thi? otjier side, 

 t Nature, July 24th, 1890, p. 290. 



