26o The Descent of Man. Fabt U 



>io6 that the whole problem is so intricate that it is safer to leava 

 its solution for the future. 



CHAPTEE IX. 



Seoomdart Sexual Chaeaotbbs in thk Lower Clabskb of 

 THE Animal Kingdom. 



Tliese characters absent in the lowest classes — Brilliant colours — MoUusca 

 — Annelids — Crustacea, secondary sexual characters strongly developed ; 

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

 sexual colours of; stridulatiou by the males — Myriapoda. 



With animals belonging to the lower classes, the two sexes 

 are not rarely united in the same individual, and therefore 

 secondary sexual characters cannot be developed. In many 

 cases where the sexes are separate, both are permanently at- 

 tached 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 Protozoa, 

 Coslenterata, Echinodermata, Scolecida, secondary sexual cha- 

 racters, 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 shghtly in colour 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 

 propagation 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 (Actiniae), some jelly-fish (Medusae, 

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

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

 namely the union of the two sexes in some of these animals, the 

 permanently affixed condition of others, and the low mental 

 powers of all, that such colours do not serve as a sexual 

 attraction, and have not been acquired through sexual selectioa 



