Chap. IX. 
SPIDERS. 
acquired through sexual selection. Fritz Muller 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, Arachnida (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 8 parassus 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. jloricolens, 
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 
12 1 Facts and Arguments/ &c., p. 79. 
13 4 A History of the Spiders of Great Britain/ 1861-64. For the 
following facts, see p. 102, 77, 88. 
YOL. I. 
Z 
