CRUSTACEANS. 299 



attracted by each other's greater beauty, might unite 

 and leave offspring which would inherit their parents' 

 greater beauty. But with such lowly-organized creatures 

 this is extremely improbable. Nor is" it at all obvious how 

 the offspring from the more beautiful pairs of hermaphro- 

 dites would have any advantage over the offspring of the 

 less beautiful, so as to increase in number, unless indeed 

 vigor and beauty generally coincided. We have not here 

 the case of a number of males becoming mature before 

 the females, with the more beautiful males selected by the 

 more vigorous females. If, indeed, brilliant colors were 

 beneficial to a hermaphrodite animal in relation to its gen- 

 eral habits of life, the more brightly-tinted individuals would 

 succeed best and would increase in number; but this would 

 be a case of natural and not of sexual selection. 



Sub -kingdom of the Venues Annelida (or Sea- 

 worms). In this class, although the sexes, when separate, 

 sometimes differ from each other in characters of such im- 

 portance that they have been placed under distinct genera 

 or even families, yet the differences do not aeem of the kind 

 which can be safely attributed to sexual selection. These 

 animals are often beautifully colored, but as the sexes do 

 not differ in this respect we are but little concerned with 

 them. Even the Nemertians, though so lowly organized, 

 " vie in beauty and variety of coloring with any other 

 group in the vertebrate series;" yet Dr. Mclntosh * cannot 

 discover that these colors are of any service. The sedentary 

 annelids become duller-colored, according to M. Quatre- 

 fages,t after the period of reproduction; and this I pre- 

 sume may be attributed to their less vigorous condition at 

 that time. All these worm-like animals apparently stand 

 too low in the scale for the individuals of either sex to exert 

 any choice in selecting a partner, or for the individuals of 

 the same sex to struggle together in rivalry. 



Sub -kingdom of the Arlliropoda Crustacea. In 

 this great class we first meet with undoubted secondary 

 sexual characters, often developed in a remarkable manner. 



*See his beautiful monograph on "British Annelids," part i, 1873, 

 p. 3. 



f See M. Perrier. " 1'Origine de I'Hoinined'apres Darwin," " Revue 

 Scientifique," Feb., 1873, j). S6. 



