16 PECKHAM. [Vol. 1, 



when the young resemble their parents, the resemblance, 

 although very strong, is not so complete as to render them 

 exactly alike. 



CLASSES OF CASES. 



I. When the adult male is more conspicuous than the 

 adult female the young of both sexes in color and form closely 

 resemble the adult female. 



II. When the adult female is more conspicuous than the 

 adult male the young of both sexes, in color and form, more 

 closely resemble the adult male than they do the adult female, 

 especially in the earlier moults. 



III. When the adult male resembles the adult female the 

 young of both sexes resemble the adults.^ 



In Darwin's discussion of the subject of sexual selection, 

 he considered in great detail how far the moulting habits of 

 birds tended to support his theory that the differences between 

 the two sexes are attributable to female selection, rather than 

 to natural selection acting upon the greater need for protection 

 on the part of the female. In his profound discussion of the 

 laws of heredity he formulates two general propositions. First: 

 That variations appearing early in the life of an organism 

 would tend to be transmitted to the offspring of both sexes. 

 Second : That variations appearing late in life would be limited 

 to the sex in which they first appeared, and would tend to ap- 

 pear at a corresponding age ; the exception being that they 

 might appear at an earlier age in the offspring than they did 

 in the first instance. When the great complexity of the sub- 

 ject is considered, and the way in which natural selection must 

 have sometimes modified sexual selection is taken into account, 

 it is remarkable how fully the moulting habits of birds con- 

 firm his generalizations ; and it is of the highest interest to in- 

 quire how far the moulting habits of spiders are also consistent 

 with them. 



Class I includes the cases where the adult male spider is 



1 These classes are slightly modified from Darwin, Descent of Man, p. 406. 



