No. 1.] SEXUAL SELECTION IN SPIDERS. 5 



ous, have the greater surplus and consequently the richer orna- 

 mentation ? 



Grant Allen, in his Colour Sense, remarks, concerning the 

 ornamental appendages of animals : "Whatever we may think 

 of their functions, we must agree that they are, on the whole, 

 products of a high vitality. They represent part of the excess 

 of nutriment over expenditure. But these dermal adjuncts do 

 not probably take away anything from the effective energies of 

 the organism." 1 He evidently understands Mr. Wallace to 

 mean that these color adjuncts are by-products, or waste, from 

 the other tissues. In this connection he quotes from Mr. Lowne 

 to the effect that " the dermal appendages of reptiles and the 

 feathers of birds, rich in pigment and nitrogen, are probably 

 entirely excrementitious to the other tissues, and, without 

 doubt, depend in great part for their origin on the solid nature 

 of the excretion of the kidneys. Birds especially, leading a 

 very active life, excrete material rich in nitrogen ; and the 

 feathers, which are shed periodically, enable them to throw 

 off that element without overtaxing their renal organs." - 

 " Hence," says Mr. Allen, " w^e can understand why the more 

 active and energetic sex should possess a greater number of 

 highly developed dermal adjuncts, and should often display 

 much brighter colors than the females." This, however inter- 

 esting it may be as a speculation, has, so far as we are aware, 

 no direct evidence to support it ; and knowing so little as we 

 do at present of the functions of the kidneys in birds, and of 



1 p. 188. 



2 The fact that closely related species annually undergo a double moult and 

 others only a single one, and that even in the same species the sexes sometimes 

 differ in their moulting habits, renders this proposition improbable, The habits 

 being usually identical, why should one species depend upon moulting for the dis- 

 posal of its surplus nitrogen, while in another the burden is borne by the excretory 

 organs alone? Is there a single anatomical fact to countenance such a supposition? 

 Darwin says that there is reason to believe that with certain bustards and rail-like 

 birds, which i^roperly undergo a single moult, some of the older males retain their 

 nuptial plumage throughout the year. In the birds of paradise some have a single 

 moult, some a double, and others, after the moult of the first year, do not cast 

 their feathers again. For other facts bearing on this habit, see Descent of Man, 

 Am. Ed., pp. 391-394. 



