FERTILITY AND THE SEXES. 17 



The second main fact on fertility ("germ strength") was developed from obser- 

 vations on the gradations which this function presents in different individuals of 

 the same species, and which it may undergo in one and the same individual. Age, 

 season, and the rate at which eggs are produced were all found to affect the heights 

 or levels of fertility in pigeons. And the two sexes were here also found to be 

 associated with fertility ("germ strength") — ^maleness with greater fertility 

 (strength), femaleness with weaker fertility. It is this aspect of fertility that is 

 referred to in the first quoted paragraph. 



From some of those crosses in which fertility was "lowered" and the resulting 

 offspring were "predominantly male" it was noted that the "occasional" females 

 more often appeared at or near the end of the season. Moreover, such results were 

 more frequently obtained in such of the matings as had produced a greater number 

 of eggs than usual, as a result of the ]irompt removal of these eggs as soon as laid 

 to other birds for incubation. In other words, reproductive overwork, in such a 

 series, tends towards the production of female offspring. Lateness of season and 

 crowded reproduction seemed each to play a part in the production of females 

 from gametes otherwise producing only or mostly male offspring. These earlier 

 indications were confirmed by later work. The body of evidence bearing on these 

 points must, of course, be presented later, but we note here the fact that often — 

 in a mating of the above sort in'which the dominance of sex is shifted during the 

 season from maleness to femaleness, under "crowded reproduction " — some embryos 

 are produced very late in the season not strong enough to break through the shell; 

 and still later, embryos are produced of fewer and fewer or of no days of develop- 

 ment. These weak germs, at this season, may proceed from a pair whose earlier 

 eggs — of spring and early summer — produced hatchable, vigorous, and long-lived 

 birds which were mostly or only males. The loss of fertility during the season ^ 

 involves, then, a progressive weakening of the germs themselves after starting 

 from a given — reduced — level of fertility (germ compatibility) produced by 

 selecting consorts of distant phylogenetic relationship. There are, then, two 

 distinct kinds of things that have been called "lowered fertility"; and the two 

 means of obtaining a low (or a high) fertility very differently affect the production 

 of sex. 



A few paragraphs — immediately following the first four given at the begin- 

 ning of this chapter — bear upon this matter of "weakened germs." They were 

 written beneath the caption: "Strength in Parents Tends to Produce Male 

 Offspring." 



"There is from pigeon crosses a preponderance of males from first eggs, and of females 

 from second eggs. The first egg of the clutch may be supposed to have the advantage, as 

 its needs are provided first, and the second egg, which is always the last of a clutch, has 

 not quite equal chances, for it does not have first chance.' 



"I think the first eggs of the season are certainly stronger than those coming late in the 

 season. Elsewhere the early birds are the ones most highly prized by breeders. In poultry 



"This Inss (il IVrtility (■■«cTm strength") is to be observed in the eggs of much "overworked" females, whether 



they arc iii:iti(l i n- ni I Inn own or of a very different species. — Editor. 



" ' Willi man untis i W '.ii lliat "The male and fem.ale have potentially the same characters. Usually the female 

 lags behind, l)ut sonictiiiics (lie male lags," .and cites Darwin's Descent of Man, Vol. II, pp. 191-199, and Beddard's 

 Animal Coloration. This subject is more fully treated in Volume I, Chajjs. V-VII. 



