344 THE DESCENT OF MAN 



CHAPTER IX 



SECONDARY SEXUAL CHARACTERS IN THE LOWER CLASSES 

 OP THE ANIMAL KINGDOM 



These characters absent in the lowest classes — Brilliant colors — Mollusoa, — 

 Annelids — Crustacea, secondary sexual characters strongly developed; 

 dimorphism; color; characters not acquired before maturity — Spiders, 

 sexual colors of ; stridulation by the males — Myriapoda 



WITH animals belonging to tlie lower classes, the 

 two sexes are not rarely united in tke same 

 individual, and therefore secondary sexual char- 

 acters cannot be developed. In many cases where the sexes 

 are separate, both are permanently attached to some support, 

 and the one cannot search or struggle for the other. More- 

 over, it is almost certain that these animals have too imper- 

 fect 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, Coelenterata, 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 ex- 

 ceptions 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 suppose that such differences have been augmented 

 through sexual selection. Contrivances by which the male 

 holds the female, and which are indispensable for the propa- 

 gation of the species, are independent of sexual selection, 

 and have been acquired through ordinary selection. 



