Chap. XV. Birds — Sexually Limited Inheritance. 445 



imaginary illustration will best aid us in seeing the difficulty oi 

 the case : we may suppose that a fancier wished to mako a 

 breed of pigeons, in which the males alone should be coloured 

 of a pale blue, whilst the females retained their former slaty 

 tint. As with jDigeons characters of all kinds are usually trans- 

 mitted to both sexes equally, the fancier would have to try to 

 convert this latter form of inheritance into sexually-limited 

 transmission. All that he could do would be to persevere in 

 selecting every male pigeon which was in the least degree of a 

 paler blue; and the natural result of this process, if steadily 

 carried on for a long time, and if the pale variations were 

 strongly inherited or often recurred, would be to make his 

 whole stock of a lighter blue. But our fancier would be com- 

 pelled to match, generation after generation, his pale blue males 

 with slaty females, for he wishes to keep the 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 tint ; for the primordial slaty 

 colour would be transmitted with prepotent force. Supposing, 

 however, that some pale-blue males and slaty females were 

 produced during each successive generation, and were always 

 crossed together ; then the slaty females would have, if I may 

 use the expression, much blue blood in their veins, for their 

 fathers, grandfathers, &c, will all have been blue birds. Under 

 these circumstances it is conceivable (though I know of no 

 distinct facts rendering 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 in the above case 

 of the desired character, 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 Scernmerrings pheasant has a tail thirty- seven 

 inches in length, whilst that of the female is only eight inches ; 

 the tail of the male common pheasant is -about twenty inches, 

 and that of the female twelve inches long. Now if the female 

 Scemmerring 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 a tail much longer than that 

 of the female Scemmerring pheasant, were crossed with the male 



