No. 1.] SEXUAL SELECTION IN SPIDERS. 25 



differ from each other according to sex, the young males resem- 

 bling the adult males, and the young females the adult females. 

 In this case the law of inheritance at corresponding ages must 

 be supposed to have failed, the young males inheriting their 

 differential peculiarities at an earlier age than that at which the 

 variation first appeared in their male ancestors. 



PhicUppus riifus, when mature, is a brick-red spider, the 

 male being considerably brighter than his consort. When 

 about one-seventh grown, and after the third or fourth moult, 

 the young are very dark brown, with light yellow legs. Some 

 moults later, they are reddish, with narrow, oblique whitish 

 bars on the sides of the abdomen, and two dark bands on the 

 dorsum, on each of wliich is a row of white dots. The appear- 

 ance of the spider changes but little during the next four 

 moults, but after the last — the tenth — -both male and female 

 become mature and acquire the adult color. The meaning of 

 the fifth moult — that with the uniform brown body and yellow 

 legs — we are unable to explain. The appearance of the female 

 after the fifth moult is similar to that of many other females 

 in the genus, and her final change is probably due to a trans- 

 ference to her of the male color, which, judging from the 

 moults, must have appeared late in life. 



All the cases under the first and third classes are intelli- 

 gible if we suppose that the females have selected the more 

 conspicuous males, and that when variations occurred late in 

 life they were limited to the sex in which they first appeared. 

 There are, however, many cases in which it is probable that the 

 color variation of the male has modified the female in a greater 

 or less degree, and this accounts for the instances m which the 

 female, as well as the male, is showily colored, especially since 

 the showy color in these females usually tends to approach the 

 coloring of the males, and to depart, in the same proportion, 

 from the normal coloring of tlie genus. The second class, in 

 which the females are more brilliant than the males, is the 

 only one in which the moulting habits of spiders are not strik- 

 ingly similar to those of birds ; and it seems in the highest 



