SEXUAL SELECTION 859 



spicuous; thus the female of Sparassus smaragdulus is dull- 

 ish green, while the adult male has the abdomen of a fine 

 yellow, with three longitudinal stripes of rich red. In cer- 

 tain species of Thomisus the sexes closely resemble each 

 other, in others they differ much; and analogous cases occur 

 in many other genera. It is often difficult to say which of 

 the two sexes departs most from the ordinary coloration 

 of the genns to which the species belong; but Mr. Blackwall 

 thinks that, as a general rule, it is the male; and Canestrini" 

 remarks that in certain genera the males can be specifically 

 distinguished with ease, but the females with great diffi- 

 culty. I am informed by Mr. Blackwall that the sexes 

 while young usually resemble each other; and both often 

 undergo great changes in color during their successive 

 moults, before arriving at maturity. In other cases the 

 male alone appears to change color. Thus the male of 

 the above bright-colored Sparassus at first resembles the 

 female, and acquires his peculiar tints only when nearly 

 adult. Spiders are possessed of acute senses, and exhibit 

 much intelligence ; as is well known, the females often show 

 the strongest affection for their eggs, which they carry about 

 enveloped in a silken web. The males search eagerly for 

 the females, and have been seen by Canestrini and others to 

 fight for possession of them. This same author says that 

 the union of the two sexes has been observed in about 

 twenty species; and he asserts positively that the female 

 rejects some of the males who court her, threatens them 

 with open mandibles, and at last, after long hesitation, 

 accepts the chosen one. From these several considerations 

 we may admit with some confidence that the well-marked 

 differences in color between the sexes of certain species are 

 the results of sexual selection ; though we have not here the 

 best kind of evidence — the display by the male of his orna- 

 ments. From the extreme variability of color in the male 



•• This author has recently published a valuable essay on the "Caratteri 

 aessuali secondarii degli Arachnidi," in the "Atti della Soo. Veneto Trentin* 

 di Sc. Nat Padova," voL L, Faso. 3, 1873. 



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