INTRODUCTION. XXV11. 



ings of the very young spider, and those which it attains after 

 one or two changes of skin ; Epeira diademata, Clerk., and Zilla 

 x-notata, Ibid., two of our commonest spiders, are conspicuous 

 examples of this. Practice, and careful observation only, will 

 enable the collector to pronounce, at a glance, upon the species 

 of a large proportion of very young spiders; whilo in some 

 groups the most experienced colloctor is unable to decide, with 

 any certainty, on the species until maturity is attained. 



Difference in Size and Colours between the Male and 

 Female Spider. 



Another difficulty in the collector's way is the great difference 

 both in size, colours, and pattern between the sexes of many 

 spiders. Excepting one spider — Argyroneta aquatica, Clerck. — all 

 those found in Great Britain have the female either equal in size, 

 or else larger than the male. The difference, however, between 

 the sexes is not, in theso northern regions carried to tho extreme 

 limits which are frequently reached in the tropics. The female 

 of Nephila ohrysogaster, Walck. (an almost universally distributed 

 tropical Epeirid) measures two inches in the length of its body, 

 while that of the male scarcely exceeds 1-1 Oth of an inch ; and is 

 less than 1-1 300th part of her weight. As an instance of great dis- 

 parity in size between the sexes of some British spiders, Misumena 

 vatia, Clerck., may be mentioned. The colours and markings 

 of the sexes differ more frequently than the size ; the spider just 

 named being a striking instance of this also. Attention is called to 

 these differences, wherever known, in the following descriptions ; 

 but in respect to new species, or to thoso spiders whose sexes are 

 not yet both ascertained, experience alone will prove the specific 

 identity of some, whose males and females may appear at first 

 sight to belong to quite distinct species. It is difficult, not to say 

 impossible, to account for very great differences in size between 

 the sexes, on any other hypothesis than that of " natural selec- 

 tion." Many Epei'rids exemplify this difference in size very strik- 

 ingly, among them the spider noted abovo — Nephila chrysogastcr 

 — is an extreme instance. It has been proved with respect to one 

 of our own commonest Epei'rids — Epeira diademata, Clerck. — and 



