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Show . 320 TilE PRINCIPLES OF SEXUAL SELECTION. PART II. some variation in their constitution produced fewer eggs or youn<Y would produce them of greater size or vigour; 0 ·and the a' dults reared from such eggs or young wou lcl mn.nifestly have the best chance of surriving,. ~nd would inherit a tendency towards lessened fert1hty. The parents, moreover, which had to nourish or provide for fewer offspring would themselves be e~posed to a less severe strain in the struggle for existence, and would have a better chance of surviving. By thes ·steps, and by no others as far as I can see, natural selection under the above conditions of severe competition for food, would lead to the formation_ of a new race less fertile, but better adapted for survival, than the parent-race. CliAP.lX . SEXUAL SELECTION. 321 CHAPTER IX. SECONDARY SEXUAL CHARACTERS I~ THE LOWER CLASSES OF THE ANIMAL KINGDOM, These characters absent in the lowest classes- Brilliant coloursMollusca- Annelids- Crustacea, secondary sexual characters strongly developed; dimorphism; colour; characters not acquired before maturity- Spiders, sexual colours of; stridulation by the males-Myriapoda. IN the lowest classes the two sexes are not rarely united in the same individual, and therefore secondary sexual characters cannot be developed. In many cases in which the two 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 t~o low mental powers to feel mutual rivalry, ·or to appreciate each other's beauty or other attractions. Hence in these classes, such as the Protozoa, Ccelenterata, Echinodermata, Scolecida, true secondary sexual characters do not occur; and this fact agrees with the Lelief that such characters in the higher classes have been acquired through sexual selection, which depends on the will, desires, 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 colour from the females ; but we have no reason to suppose that such differences have been augmented through sexual selection. VOL. I. y |