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Show 308 THE PRINCIPLES OF PART II. are many difficulties in arriving at any just conclusion~l· !~fer~le females might readily be mistaken for males, as Dr.. un er as remarked to me in regard to trout. With some s~eCles the ma~es are believed to die soon after fertilising the ova. Wrth many sp~c~'~s the males are of much smaller size thau the females, so tha~_a h arle number of males would escape from the same net ~y w rc t 1e females were caug ht· 1.n\1 ( • Carbonnier ' 52 who has espeCiallyh attended to the natural history of the pike (Esox lucius) states t _at man~ l · rr to their small size are devoured by the larger females, rna es, owrno ' h , d f · and he believes that the males of almost all fis are expose rom tl e Cause to rrreater danCYer than the females. Nevertheless 1e sam ' o o . b . h b in the few cases in which the proportwnal nu~ ers ave , een aetnal l y ob s erve d , the males appear to be largely m exfci elsds . 'I hu.. s Mr. R. Buist, the superintendent of the Stormont e expen-t that lmen s, says ·n 1865 , out of 70 salmon first landed for the of obtainin(f the ova upwards of 60 were males. 1n 1p8ur6p7o shee again "calol s attentio' n to t h e vas t d"r spropor t" f the 1011 o "males to the females. We had at the outset at least t_e~ males "to one female." Afterwards sufficient females for ob~ammg ova red He adds " from the great proportion of the w~~oo. ' h "males they are eonstantly fighting and tearing each other on t e "spaw~ing-beds."53 'This disprop~rtion, no doubt, can be accounted for in part, but whether wholly rs very doubtful, by the males ascending the rivers before the females. Mr. F. Buckland remarl\s in regard to trout, that " it is a curious fact that the mal~s pre?on" derate very largely in number over the females. It wvanably " happens that when the first rush of fish is made to the net, t~ere " will be at least seven or eight males to one female found captrve. "I cannot quite accotmt for this; either the males are more numer" ous than the females, or the latter seek safety by conce~lment "rather than flight." He then adds, that by carefully searchmg the banks, sufficient females for obtaining ova can be.found.5~ .Mr. H. Lee informs me that out of 212 trout, taken for th1s purpose m Lord Portsmouth's park, 150 were males and 62 females. . With the Cyprinidm the males likewise seem to be m excess ; but several members of this Family, viz., the carp, tench, bream and minnow, appear regularly to follow the practice, rare in the . 11 Leuckart quotes Bloch (Wagner, 'Handworterbuch der Phys.' B. iv. 1853, s. 775), that with fish th ere are twice as many males as females. 52 Quoted in the' Farmer,' March 18, 1869, p. 369. , 53 'The Stormontfield Piscicultural Experiments,' 1866, p. 23. 'I he 'Field' newspaper, June 29th, 1867. 54 'Land and Water,' 1868, p. 41. CHAP. VIII. SEXUAL SELECTION. 309 animal kingdom, of polyandry; for the female whilst spawning is always attended by two males, one on each side, and in the case of the bream by three or four males. 'This fact is so well known, that it is always recommended to stock a pond with two male tenches to one female, or at least with three males to two females. With the minnow, an excellent observer states, that on the spawningbeds the males are ten times as numerous as the females ; when a female comes amongst the males," she is immediately pressed closely " by a male on each side; and when they have been in that situa tion for a time, are superseded by other two males." 55 INSECTS. In this class, the Lepidoptera alone afford the means of judging of the proportional numbers of the sexes; for they have been collected with special care by many good observers, and have been largely bred from the egg or caterpillar state. I had hoped that some breeders of silk-moths might have kept an exact record, but after writing to France and Italy, ancl consulting various treatises, I cannot find that this has ever been done. The general opinion appears to be that the sexes are nearly equal, but in Italy as I hear from Professor Canestrini, many breedt-rs are convinced that the females are produced in excess. The same naturalist, however, informs me, that in the two yearly broods of the Ailanthus silkmoth (Bombyx cynthia), the males greatly preponderate in the first, whilst in the second the two sexes are nearly equal, or the females rather in excess. In regard to Butterflies in a state of nature, Reveral observers have been much struck by the apparently enormous preponderance of the ruales.66 Thus Mr. Bates/7 in speaking of the species, no less than about a hundred in number, which inhabit the Upper Amazons, says that the males are much more numerous than the females, even in the proportion of a hundred to one. In North America, Edwards, who had great experience, estimates in the genus Papilio the males to the females as four to one; and Mr. 55 Yan·ell, 'Hist. British Fishes,' vol. i. 1836, p. 307 ; on the Cyprinus carpio, p. 331; on the Tinea vulgaris, p. 331; on the Abramis brama, p . 336. See, for the minnow (Leuciscus phoxinus), 'Loudon's Ma"'. of Nat. Hist.' vol. v. 1832, p. 682. "' 56 Leuckart quotes Meinecke (Wagner, 'Handworterbuch der Phys.' B. iv. 1853, s. 775) that with Butterflies the males are three or four times as numerous as the females. 57 'The Naturalist on the Am:tzons,' vol. ii. 1863, p. 228, 347. |