FERTILITY AND THE SEXES. 19 



Color, like sex, is to some extent involved in this flux of strength of germs. 

 Dark and white, at any rate, are sometimes thus involved; dark color being the 

 more closel.y associated with strong germs, whiteness more often associated with 

 weak germs, though instances of sex-limited color inheritance were found Avhich, 

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



A statement may be made at this point concerning the author's 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 he had assured himself 

 of the incompleteness or inadequacy of Mendelian and representative particle 

 conceptions of heredity,'" and therefore preferred, in such instances, not to use 

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

 seasonal change from males to females there is a real reversal or change in the 

 sex-potency of the individual germs, due to or in accord Avith the weakening effects 

 which (as fertility) he had repeatedly observed and partially analyzed; that is to 

 say, a given pair of germ-cells which, if matured and united under one set of condi- 

 tions (strength) will produce a male, can be made under another set of conditions 

 (weakness) to give rise to a female. 



The author of course thoroughly appreciated the possibility that selective 

 fertilization, differential maturation, and selective mortality of ova in the ovary 

 might conceivably here be operative, and that one or all of these would be appealed 

 to by others, who had not seen all that he had seen, to account for this "shifting 

 of dominance" or apparent sex-reversal. Nor did he permit himself a definite or 

 final decision of the question of sex-reversal. 



The evidences within the " shif ting-of-dominance " series itself, which to him 

 most strongly suggested real sex-reversal as the correct interpretation of the series, 

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

 power of the germs of these same series from spring to autumn — sometimes a nearly 

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

 embryos, and embrj-os of fewer and fewer days of development, to a point of very 

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

 birds arise from the earlier, stronger germs than from the later and latest ones. 

 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 holds 

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



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

 or domestic pigeons some of the "weakening" effects of overwork at egg-laying 

 have been recognized by breeders of these forms: 



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

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

 sometimes show no signs of doing so until March, whilst if it be mild some birds, if allowed, 

 would go to nest in January. This, however, the owner should in all cases prevent, by 

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



'» See Chapter XIV. 



" Fulton's Book of Pigeons. London, 1895. The quotation given was indicated by means of a page reference 

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



