Chap. IX. SPIDERS. 337 



acquired through sexual selection. Fritz Miiller 12 gives 

 some striking instances of this law ; thus the male 

 sand-hopper (Orchestia) does not acquire his large 

 claspers, which are very differently constructed from 

 those of the female, until nearly full-grown ; whilst 

 young his claspers resemble those of the female. Thus, 

 again, the male Brachyscelus possesses, like all other 

 amphipods, a pair of posterior antennae ; the female, 

 and this is a most extraordinary circumstance, is desti- 

 tute of them, and so is the male as long as he remains 

 immature. 



Class, Araclmida (Spiders). — The males are often 

 darker, but sometimes lighter than the females, as may 

 be seen in Mr. Blackwall's magnificent work. 13 In 

 some species the sexes differ conspicuously from each 

 other in colour ; thus the female of Sjparassus sma- 

 ragdulus is dullish-green ; whilst the adult male has 

 the abdomen of a fine yellow, with three longitudinal 

 stripes of rich red. In some species of Thomisus the 

 two sexes closely resemble each other ; in others they 

 differ much; thus in T. citreus the legs and body of 

 the female are pale-yellow or green, whilst the front 

 legs of the male are reddish-brown : in T. Jiorieolens, 

 the legs of the female are pale-green, those of the 

 male being ringed in a conspicuous manner with various 

 tints. Numerous analogous cases could be given in the 

 genera Epeira/Nephila, Philodromus, Theridion, Liny- 

 phia, &c. 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 



f 



12 ' Facts and Arguments,' &c., p. 79. 



13 'A History of the Spiders of Great Britain,' 18<»1-G4. For thc 



following facts, see p. 102, 77, 8S. 

 VOL. I. 



