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Show 338 SEXUAL SELECTION. PART II. thinks that, as a general rule, it is the male. Both sexes whilst young, as I am informed by the same author, usually resemble each other; an~ both of~en 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-mentioned brightly-coloured Sparassus at first resembles the female and acquires his peculiar tints only when nearly a~u!t. Spide.rs a1~e possessed of acute senses, and exhibit much mtelhgence. The females often ~hew, as is r:ell known, the strongest affection for their eggs, whwh they carr! about enveloped in a silken web. . On the ~hole It appears probable that well-marked differences m colour between the sexes have generally resulted from sexual selection, either on the male or female side. But doubts may be entertained on this head from the extreme variability in colour of some species, for instance of Theridion lineatum, the sexes of which differ when adult ; this great variability indicates that th~ir colours have not been subjected to any form of selectwn. Mr. Blackwall does not remember to have seen the males of any species fighting together for the possession of the female. Nor, judging from analogy, is this probable; for the males are generally much smaller than the females, sometimes to an extraordinary degree. 14 Had the males been in the habit of fighting together, they would, it is probable, have gradually 14 Aug. Vinson (' Araneides des Iles de la Reunion,' pl. vi. figs. 1 <t::ld 2) gives a good instance of the small size of the male in Epeira nigra. In this species, as I may add, the male is testaceous and the female black with legs banded with red. Other even more striking cases of inequality in size between the sexes have been recorded ('Quarterly Journal of Science,' 1868, July, p. 429); but I have not seen the original accounts. CnAP. IX. SPIDERS AND MYRIAPODA. 339 acquired greater size and strength. Mr. Blackwall has sometimes seen two or more males on the same web with a single female ; but their courtship is too tedious and prolonged an affair to be easily observed. The male is extremely cautious in making his advances, as the female carries her coyness to a dangerous pitch. De Geer saw a male that "in the midst of his preparatory ~' caresses was seized by the o~ject of his attractions, "enveloped by her in a web and then devoured, a "sight which, as he adds, filled him with horror and "indignation." 15 West ring has made the interesting discovery that the males of several species of Theridion 16 have the power of making a stridulating sound (like that made by many beetles and other insects, but feebler), whilst the females are quite mute. The apparatus consists of a serrated ridge at the base of the abdomen, against which the hard hinder part of the thorax is rubbed; and of this structure not a trace could be detected in the females. From the analogy of the Orthoptera and Homoptera, to be described in the next chapter, we may feel almost sure that the stridulation serves, as Westring remarks, either to call or to excite the female ; and this is the first case in the ascending scale of the animal kingdom, known to me, of sounds emitted for this purpose. Class, l.Iyriapoda.-ln neither of the two orders in this class, including the millipedes and centipedes, 15 Kirby and Spence,' Introduction to Entomology,' vol. i. 1818, p. 280. 16 Theridion (Asagena, Sund.) serratipes, 4-puuctatum et guttatum; see Westring, in Kroyer, 'Naturhist. Tidskrift,' vol. iv. 1842-1843 p. 3:1:9; and vol. ii. 1846-1849, p. 342. See, also, for other species' ' Aranero Svecicce,' p. 184. . ' z 2 |
