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Show 156 SEXUAL SELECTION : BIRDS. PART ID. latter of this colour. The result would generally be the production either of a mongrel piebald lot, or more probably the speedy and complete loss of the pale-blue colour, for the primordial slaty tint would be transmitted with prepotent force. Supposing, however, that some pale-blue males and slaty females wore produced clurjng each successive generation, and were always m·ossed together; then the slaty females would have, if I may use the expression, much blue blood in then· veins, for their fathers, grandfathers, etc., will all have been blue birds. Under these circumstances it is conceivable (though I know of no distinct facts renderin()' . b It probable) that the slaty females might acquire so strong a latent tendency to pale-blueness, that they would not destroy this colour in their male offspring, their female offspring still inheriting the slaty tint. If so, the desired end of making a breed with the two sexes permanently different in colour might be gained. The extreme importance, or rather necessity, of the desired character in the above case, namely, pale-blueness, being present though in a latent state in the female, so that the male offspring should not be deteriorated, will be best appreciated as follows: the male of Soommerring's pheasant has a tail thirty-seven inches in length, whnst that of the female is only eight inches; ~he tail of the male col!lmon pheasant is about twenty ~nches, and that of the female twelve inches long. Now If the female Soommerring pheasant with her short tail were crossed with the male common pheasant, there can be no doubt that the male hybrid offspring would have a much longer tail than that of the pure offspring of the common pheasant. On the other hand, if the female common pheasant, with her tail nearly twice as long as that of the female Soommerring pheasant, were crossed with the male of the latter, the male hybrid off:lpring t'nAP. XV. SEXUALLY-LIMITED INHERITANCE. 157 would have a much shorter tail than that of the pure .Qffspring of Soommerring's pheasant.3 Our fancier, in order to make his new breed with the males of a decided pale-blue tint, and the females unchanged, would have to continue selecting the males during many generations ; and each stage of palenef:S would have to be fixed in the males, and rendered latent in the females. The task would be an extremely difficult one, and bas never been tried, but might possibly succeed. The chief obstacle would be the early and complete loss of the pale-blue tint, from the necessity of reiterated crosses with the slaty female, the latter not having at first any latent tendency to produce pale-blue offspring. On the other hand, if one or two males were to vary ever so slightly in paleness, and the variations were from the first limited in their transmission to the male sex, the task of making a new breed of the desired kind would be easy, for such males would simply have to be selected and matched with ordinary females. An analogous case has actually occurred, for there are breeds of the pigeon in Belgium 4 in which the males alone are marked with black strim. In the case of the fowl, variations of colour limited in their transmission to the male sex habitually occur. Even when this form of inheritance prevails, it might well happen that some of the successive steps in the process of variation might be transferred to the female, who would then come to resemble in a slight degree the male, as oecurs in some breeds of the fowl. Or again, the greater number, but 3 Temminck says that the tail of the female Phasianus Sremmerringii ir; only six inches long, 'Planchcs colorices,' vol. v. 1838, p. 487 and 488: tho measurement!:! above given were made for me by Mr. Sclater. For the common pheasant, sec Macgillivray,' Hist. Brit. Birds,' vol. i. p. ll8-121. 4 Dr. Ohapuis, 'Le Pigeon Voyageur Bclg:c,' 18G5, p. 87. • |