294 THE DESCENT OF MAN. 



CHAPTER IX. 



SECONDARY SEXUAL CHARACTERS IN THE LOWER CLASSES 

 OF THE ANIMAL KINGDOM. 



These characters absent in the lowest classes Brilliant colors 

 Molltisca Annelids Crustacea, secondary sexual characters 

 strongly devoloped; dimorphism; color; characters not acquired 

 before maturity Spiders, sexual colors of; stridtilatioii by the 

 males Myriapoda. 



WITH animals belonging to the lower classes, the two 

 sexes are not rarely united in the same individual, and there- 

 fore secondary sexual characters cannot be developed. In 

 many cases where the sexes are separate both are perma- 

 nently attached to some support, and the one cannot search 

 or struggle for the other. Moreover it is almost certain 

 that these animals have too imperfect senses and much too 

 low mental powers to appreciate each other's beauty or 

 other attractions, or to feel rivalry. 



Hence in these classes or sub-kingdoms, such as the Pro- 

 tozoa, Ccelenterata, Echinodermata, Scolecida secondary 

 sexual characters of the kind which we have to consider do 

 not occur; and this fact agrees with the belief that such 

 characters in the higher classes have been acquired through 

 sexual selection, which depends on the will, desire and 

 choice of either sex. Nevertheless some few apparent 

 exceptions occur; thus, as I hear from Dr. Baird, the males 

 of certain Entozoa or internal parasitic worms differ slightly 

 in color from the females; but we have no reason to sup- 

 pose that such differences have been augmented through 

 sexual selection. Contrivances by which the male holds 

 the female, and which are indispensable for the propaga- 

 tion of the species, are independent of sexual selection, and 

 have been acquired through ordinary selection. 



Many of the lower animals, whether hermaphrodites or 

 with separate sexes, are ornamented with the most brilliant 

 tints, or are shaded and striped in an elegant manner; for 

 instance, many corals and sea-anemones (Actinias), somo 



