EFFECT OF SEASON OF HATCHING UPON DISTRIBUTION OF FERTILITY. 57 



In this series, from a single season, there are 19 birds which Uved long enough 

 normally to seek expression of their sexuality. They arose from a series of 30 eggs 

 (table 27). They are the result of inbreeding together with "overwork," and (for 

 some of them) late season. All of these factors are seen elsewhere, as well as here, 

 to produce weakened germs. In this case, moreover, it would seem (1) that develop- 

 mental power ivas bestowed upon this family sufficient to produce fidly fertile females, 

 hut insuffirirnt to produce fulli/ fertile mrdcR: (2) th(d nnly those fpm(des that arose 

 from the sIrniK/cr earlier germs ircrc jiasscsscd of hi<ih, fidl. nr cniii/ihlc nprodncllre 

 power. Ill ()tlu>r words, femalis (inly in this family oxhihit the function of fertility 

 unreduced ; and only those particular females which were obtained from the stronger 

 earlier eggs of an overworked female parent exhibit an unreduced or but slightly 

 reduced fertility ; their sisters from the weaker germs of late in the season show less 

 fertility or no fertility. This differential of fertility for the sexes was an unexpected 

 though probably a significant result. 



Perhaps if this situation were stated in terms of Professor Whitman's views on 

 fertility, season, and of the relation the sexes bear to each other it would be simply 

 this: The mating of related birds results in weakened offspring; the function of 

 fertility suffers with other functions — it too is weakened; the effects of overwork 

 and of lateness of season progressively accentuate this weakness. It would seem 

 from the data of this chapter, that where fertility is much reduced from these 

 sources,^ fully equipped females though not complete males'* may be produced; 

 and that this may possibly have a bearing on the author's thesis that "the male 

 goes (and must go) further in development than does the female"; or, again (if 

 the present data were sufficient for a generalization), where developmental energy, 

 from such a reason, is not of normal strength, females may be produced without 

 obvious defect, but males then produced may bear obvious defect. 



It may seem to some that there is here a contradiction of certain aspects of 

 the principle of "reduced fertility in proportion to width of cross" which has been 

 established in earlier chapters; for it was there found that the crosses of most 

 widely separated species yield only or almost exclusivelj^ males, and that fertility 

 is usually reduced in proportion to the width of crosses. In those cases too the 

 individuals with rudimentary sex-glands were the occasional /emaZfs, not the males. = 

 All is made clear, however, when one distinguishes, as has been done in Chapter III, 

 between the two very different means of reducing the "fertility" of germs. In 

 obtaining males from the "wide crosses," the "strongest" germs of the birds are 

 utilized; and apparently there is here, as in the crossing of varieties, additional 

 "strength" obtained by the mere act of crossing. The reduction of fertility which 

 pertains to such wide crosses rests upon some "incompatibility," or lack of coordi- 

 nation, of the two fused plasms, while the reduced "fertility" which is patent in 

 the data noAv under consideration rests certainly upon a very different basis — 

 upon "weakness" in fact. Here parents begin by supplying germs at once "weak- 

 ened" by a union with a related (inbred) germ; in addition, too rapid work at 



■^ 'I'liril i^, inl>rrcilini; nnd lateness of season associated with ovenvorlc. 



' l;i(( III (|ii,iiii]i;in\r studies on sex in pigeons by the editor go very far toward estabhshing the proposition 

 tliat males aiv iini mily less likely to be produced, under the extreme conditions referred to here, but those which do 

 arise are less "masculine" than are other males. 



5 Note that in the family under consideration, 1 male, from the end of the season had only a single testicle. 



