Chap. IX.] SPIDERS. 327 



males in the larger size of their chelae. In some species 

 of the genus, probably in all, the sexes pair and inhabit 

 the same burrow. They are also, as we have seen, highly- 

 intelliofent animals. From the various considerations it 

 seems highly probable that the male in this species has be- 

 come gayly ornamented in order to attract or excite the 

 female. 



It has just been stated that the male Gelasimus does 

 not acquire his conspicuous colors until mature and nearly 

 ready to breed. This seems the general rule in the whole 

 class with the many remarkable differences in structure 

 between the two sexes. We shall hereafter find the same 

 law prevailing throughout the great sub-kingdom of the 

 Vertebrata, and in all cases it is eminently distinctive of 

 characters which have been acquired through sexual se- 

 lection. 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 con- 

 structed from those of the female, until nearly full grown ; 

 while 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 destitute 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. BlackwalFs magnificent work. 13 In some spe- 

 cies the sexes differ conspicuously from each other in col- 

 or; thus the female of Sparassus smaragdulus is dullish 

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

 yellow, with three longitudinal stripes of rich red. In 



12 ' Facts and Arguments,' etc., p. 79. 



:3 'A History of the Spiders of Great Britain,' 1861-18G4. For the 

 following facts, see pp. 102, 77, 88. 



