SEXUAL SELECTION. 257 



CHAPTER IX. 



SECONDARY SEXUAL. CHARACTERS IN THE LOWER 

 CLASSES OF THE ANIMAL KINGDOM. 



These characters absent in the lower classes— Brilliant colors— Mol- 

 lusca— 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 the lower classes, the two sexes 

 are not rarely united in the same individual, and therefore sec- 

 ondary sexual characters 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. 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 clases or sub-kingdoms, such as the Protozoa, 

 Coelenterata, Echinodermata, Scolecida, secondary sexual charac- 

 ters, 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 de- 

 pends 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 suppose that such differences have been augmented through 

 sexual selection. Contrivances by which the male holds the fe- 

 male, and which are indispensable for the propagation of the 

 species, are independent of sexual selection, and have been ac- 

 quired 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 (Actiniae), some jelly-fish (Medusse, 

 Porpita, &c.), some Planaris, many star-fishes. Echini, Ascidians, 

 &c.; but we may conclude from the reasons already indicated, 

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