FERTILITY AND Till - . . ,g 



Color like sex is to some extent involved in this flux oi -I, of K , 



Dark and white, at any rate, are sometimes thus involved; ,l:,rk color I,. 



more closely associated with strong germs, nrhHenen more often : , -iatnl with 



weak germs though instances of sex-limited color inheritance u,r, f,,,,,,,| whieh 

 apparently at least, do not at all conform to this rule 



A statement may be made at this point concerning the authort interpretation 

 of this seasonal change of fertility, sex, and color. Neither of these did he ever 

 refer to as a "shifting of dominance," partly because I,.- had , 

 of the incompleteness or inadequacy of Mendelian and representative ,<art,,-|, 

 conceptions of heredity, 10 and therefore preferred, in such instances, not to 

 that terminology; partly also because his data inclined him to believe that in 

 seasonal change from males to females there is a real reversal or chanue j, ; 

 sex-potency of the individual germs, due to or in aeeord with the ueakening -ff 

 which (as fertility) he had repeatedly observed and partially analywd; tl 

 say, a given pair of gerrn-cells which, if matured and united mnl. ;il |j. 



tions (strength) will produce a male, can be made under another eel of r..n.lii. 

 (weakness) to give rise to a female. 



The author of course thoroughly appreciated the po.-.-ibility that -elective 

 fertilization, differential maturation, and selective mortality of ova in th- 

 might conceivably here be operative, and that one or all of tlie.-e would be appealed 

 to by others, who had not seen all that he had seen, to account for thi- .-hiftinu 

 of dominance" or apparent sex-reversal. Nor did he permit him.-elf a detinit. 

 final decision of the question of sex-reversal. 



The evidences within the "shifting-of-doininance" series it-elf, which to him 

 most strongly suggested real sex-reversal as the correct interpretation of th. 

 were: (1) the demonstration that there is a gradual diminution in developnie: 

 power of the germs of these same series from spring to autumn sometin rly 



continuous line along which are strung males, males and females, female-, female 

 embryos, and embryos of fewer and fewer days of development, to a point of \ 

 little or no development; (2) the demonstration that stronger and longer-lived 

 birds arise from the earlier, stronger germs than from the later and late-t < 

 This latter result he has himself noted only in cross-bred series. The attention 

 of the reader will often be drawn to this matter in the case of the wider crosses; 

 moreover, since all the records have been summarized and the longevity data put 

 in place by the editor, it has become apparent that to an extent the same fact hold.- 

 true in the overworked pure-bred series as well as in the cross-bred 



The following quotation from Lumley " (p. 35) will show that amon. 

 or domestic pigeons some of the "weakening" effects of overuorl. .-laying 



have been recognized by breeders of these forms: 



"Fancy pigeons generally show an inclination to mate together some time in tin- month 

 of February; but much depends upon the temperature, as in very -even- weather they will 

 sometimes show no signs of doing so until March, whilst if it he mild some !>ird-. if all.iv 

 would go to nest in January. This, however, the owner should in all can- prevent. In- 

 keeping the sexes separate, for several reasons. In the first [.lace, though it is possible the 



10 See Chapter XIV. 



" Fulton's Book of Pigeons. London, 1895. Thrquoi: 

 by the author; it was not copied into the author's manuscript EDITOR. 



