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Show (i SEXUAL SELECTION. ]>ART II. the temporary hook-like structure serves to strengthen and protect the jaws, when one malo charges another with wonderful violence ; but the greatly developed teeth of the male American salmon may be compared with the tusks of many mnJo mammals, and they indi ·ate an offensive rather than a protecti\'e purpo ·e. Tho salmon is not the only fish in which the teeth differ in the two sexes. Thi:; is the case with many rays. In the thornback (llaia clavata) the atlult malo· has sharp, pointed teeth, directed backwards, whilst those of tho female are broad and ilat, forming a pavement; so that these teeth differ in the two sexes or the amo species more than is usual in distinct genera of th same family. 'l'he teeth of the male become sharp only when he is adult: whilst young they are broad and flat like those of the female. As so frequently occurs with secondary sexual characters, both sexe' of some species of mys, for instance R. batis, possess, when adult,. sharp, pointed teeth ; and here n. character, proper to and primarily gained by the male, appears to have bcell tnm. mitted to the off':-;pring of both sexes. ':Jlhc teeth are likewise pointed in both exes of R. mac~data, but only when completely adult; the males acquiring them at an earlier age than the females. We shall hereafter meet with analogous cases with certain birds, in which the male acquires tho plumage common to both adult sexes, at a somewhat earlier age than tho female. vVith other species of rays the males even when old. neYor po sess sharp teeth, and consequeutly both sexes when adult are provided with broad, flat teeth like those of the young, ancl of the mature females of the above-mentionetl specics.0 As the rays aro uo1cl, 0 , co Ynrroll's account of the Rays in his 'Hist. of Briti~h FiJ;hcs,•· vol. ii. 183U, p. ':l.lG, witllan excellent figure, and p. 422, •.1::32. CuAP. xrr. FISHES. 7 strong and voracious fishes, we may suspect tl1at the males require their sharp teeth for fio-htina with their . 1 0 0 nva s; but as they l)Ossc s many parts modified and ncbptcd ~or the prehension of the female, it is po:;sible that then· teeth ma.y be used for thi purpose. In regard to size, l\'L Oarbonnier 10 maintains that with almost all fishes the female i. larger than the male; nnd Dr. G linther doe.:; not know of a sino1e in tan co in which the male is actually larger thnn °the female. vVith some Cyprinodonts the male is not even half as large as the female. As with many kinds of fishes the males habitually fight together; it is surprising that tbey have not generally become throngh the effects of sexual selection larger and stronger than the females. The males suffer from their small size for accordino- to 1\f. Car bonnier. they are li.able to be 'devoured hy 0 the females of theu own speCies when carnivorous and no doubt by other species. Increased size mu~t be in some manner of more importance to the females than :-::trcngth and size are to the males for .fio·htin;. with othe~· males; ;mel this perl1aps is to allow "of th~ proclnctwn of a vast number of ova. !n many species the male alone is ornamented with lmght colours ; or these arc much brighter in the male t~an the female. The male, a1Ho, is sometimes provided w:th appendages which appear to be of no more use to l11m for the ordinary purposes of life than arc the tailfcathe~ ·s to the peacock. I am indebted for most of the f'fo]l lowm.g facts to the great kindness of D r·. G u·· n tl 1er·. . 1 er~ IS reaso~ to suspect that many tropical fishes dtffer se~u~Uy 111 colour and tructure ; and there arc sao mlle' stnkmo0 · cases with our British fisl1es Tb 1 • e ma 0 a wnym,us lyra has been called the gemrneous dragonet 10 As quoted in 'Tho Farmer,' 18G8, p. 3G9. |