272 The Descent of Man. Pakt II. 



which are very differently constructed from those of the female; 

 whilst young, his claspers resemble those of the female. 



Class, Arachnida (Spiders). — The sexes do not generally differ 

 much in colour, but the males are often darker than the females, 

 as may be seen in Mr. Blackwall's magnificent work. 18 In some 

 species, however, the difference is conspicuous : thus the female 

 of Sparassus smaragdulus is dullish green, whilst the adult male 

 has the abdomen of a fine yellow, with three longitudinal stripes 

 of rich red. In certain 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 genus to which the species belong ; but Mr. Blackwall 

 thinks that, as a general rule, it is the male ; and Canes trim" ia 

 remarks that in certain genera the males can be specifically dis- 

 tinguished with ease, but the females with great difficulty. I am 

 informed by Mr. Blackwall that the sexes whilst young usually 

 resemble each other ; and both often undergo great changes in 

 colour during their successive moults, before arriving at maturity. 

 In other cases the male alone appears to change colour. Thus 

 the male of the above bright-coloured Sparassus at first re- 

 sembles 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 shew 

 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 colour 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 

 ornaments. From the extreme variability of colour in the male 

 of some species, for instance of Theridion lineatum, it would 

 appear that these sexual characters of the males have not as yet 

 become well fixed. Canestrini draws the same conclusion from 



18 ' A. History of the Spiders of ' Caratteri sessuali secondarii degli 

 Great Britain,' 1861-64. For the Arachnidi,' in the 'Atti deila Soc 

 following facts, see pp. 77, 88, 102. Veneto-Trentina di Sc. Nat. Padova, 



19 This author has recently pub- vol. i. Fasc. 3, 1873. 

 lished a valuable essay on the 



