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Show 1] SEXUAL SELEC'fiON. PAUl' 11. ma1 w h1. cl 1 a1· e •"• b ent in the" female. These tentacle~ a.ro ;rolongations of t1le true skin, a.ncl therefore .arc not hon!ologou with tho stifflwirs of tho former spocws; hnt it can hardly bo douutecl that both ~er:e ~he same urpose. \\"hat this purpose may be It IS dlffi nlt to ~onjecturo ; ornament docs no~ her~ seem prob~ble, but we 'can hardly suppose that stl:ff hau·s and flexible filaments can be useful in any ordinary way to the males a1 o ne. The Monacanthus sco1r.-Jas, wl1ich was shewn to m1o in the British Museum by Dr. Gunther, prese~ts a ne~r y analogous case. 'l'he male has a du~ter of stiff, s~rmght · l'ke t1·1 spmes, 1 t ose of <a comb ' on the s1des of the ta1l; • aud these in a specimen six inches long were nearly an 111ch and a half in length; the female has on the sa1~e place a cluster of bristles, which may be compared w1th .~hose of a tooth-brush. In another species, theM. perom~, the. male has a brush like that possessed by the fc1uale of tho last species, whilst the sides of the tail in the fCI:1alc arc smooth. Iu some other species the same part oi tho tail can be perceived to be a little roughened in tl~c male and perfectly smooth in the female ; ancl lastly Ill others, both sexes have smooth sides. In that strange monster the Chirnmm rnonstrosa, the male has a hooks1mped bone on the top of the head, direct:d for:vardP, with its rounded end covered with sharp spmes ; m the female "this crown is altogether absent," but whnt its usc may be is utterly unknown.17 'l'hc struetures as yet referred to are permanent in the male ufter he has arrived at maturity ; but with some Blennies and in another allied genus 18 a erest is doveloped on the head of the male only during the breed- 1; "E'. Buckland, iu 'Land aml Wn,tcr,' July, 1868, IJ· 371, "ilh !1 Ji.!:lll'C, ' 1s Dr. G unthcr, 'Catalogue of Fi<hcs,' vol. iii. p. 221 and 24.0. CIIAl'. xrr. FISIIES. 13 ing-season, and their bodi('s at the same time become more brightly-coloured. 'l'hcre can Le little doubt thnt this crest serres rts a temporary sexual ornament, for tho female docs not exhibit a tnwe of it. In other species of the same genus both sexes po. sess a crest, and in at least oue species neither sex is thus provided. In this cnse and in that of the l\Ionttcanthus, we have good instanc -s to how great an extent the sexual characters of closoly-alliocl forms may differ. In many of the Chromidm, for instance in Geophngus and especially in Oichla., the males, as I hear from Professor Agassiz/9 have a conspicuous protubernnce on the forehead, which is wholly wanting in the fem::tles and in the young males. Profes -or Agassiz adds, "I have often observed these fishes •: at the time of spawning when the protuberance is ·'largest, and at other seasons when it is totally "·anting "and tho two sexes shew no difference whatever in the "outline of the profile of the bend. I never could "ascertain that it subserves any special function, and "the Indians on the Amazon know nothing about its "u e." These protuberances in their periodical appearance resemble the fleshy carnncles on the heads of certain birds; but whether they sel'\'e as ornaments must remain at present doubtful. The males of those fishes, wltic:h differ permanently in colour from the females, often become more brilliant, as I hear from Professor Agassiz and Dr. GUnther, during the breeding-season. This is likewise the case with a multitude of :fishes, the sexes of which at all other sensons of the year are iclentical in colonr. The tench, roaeh, and perch may be given us instances. The male sn1mon at this season is "marked on the cheeks with 10 cc nlso 'A Journey in Bruzil,' by Prof. nnd 1\frs. Agassiz, 18G3, p. 220. |