18 INHERITANCE, FERTILITY, AND SEX IN PIGEONS. 



generally we expect to get the best results from the earlier lairds hatched, and fewer failures 

 occur in early settings than in later.''^ (R 16). 



With these several statements before us it is possible to approach more closely 

 to an understanding of the author's whole view of fertility, and to see that the two 

 lines of fact which he developed concerning it are consistent, though at a glance 

 w^e seem to say, first, that "lowered fertility" tends to the production of males, 

 and second that "lowered fertility" tends to produce females. 



The facts are that so long as we operate upon the function of fertility merely 

 by a choice of consorts — and this on a basis of close or distant phylogenetic relation- 

 ship — then the more we reduce the fertility the higher the proportion of male 

 offspring, and the series runs thus: 



(1) In normal fertility the sexes are about even. 



(2) In lowered fertility males predominate. 



(3) In much lowered fertility only males are produced. 



(4) From the lowest fertility no offspring de\ elop. 



If, however, we take a pair of birds from groups (2) or (3) of the above scheme 

 (and this will usually mean doves from different genera or subfamilies) and further 

 study and analyze the genetic possibilities of this pair, we find that over and above 

 the fertility incident to such a mating per se this degree of fertility is influenced 

 by season, age, health, and reproductive work. And, associated with "lateness of 

 season" and "reproductive overwork" there occurs an obvious decrease in fertility 

 (developmental power) caused, not as in the preceding series, through relative 

 "incompatibility of germs," but by a progressive weakening of germs; and the initial 

 "lowered fertility" plus this weakening of germs, may produce females. Each sex 

 predominates when its characteristic fertility level exists. 



No. (3) of the above series if thus amplified and w-ritten in terms of this second 

 series of facts would stand as follows: 



Much lowered fertility ^ + strong germs = nearly all inales. 



Much lowered fertility + medium strong germs = sexes about eciual. 



Much lowered fertility + weaker germs = females. 



Much lowered fertility + weakest germs = no development. 



' "De Vries holds that species are separated by absolute gaps, that can not be closed up. They arise by jumps 

 or as sports. Were this the case, we ought to see sudden gaps in 'fertihty.' I find that fertility is a thing of degrees, 

 i.e., it is at an optimum within the species, but it diminishes gradually — not by steps — as we pass from the crosses 

 between species closely related to crosses of species wide apart. Examples of such a series are the following: White 

 and blond ring; Japanese ring and blond ring; blond ring and Chinese ring; blond ring and European turtle; blond 

 ring and Surate turtle; blond ring and homer. And similar to the last named, blond ring and Ectopisles; white or 

 blond ring and mourning-dove; blond ring and white-wing; common pigeon and Japanese turtle." (These five last- 

 named crosses are all oi family or of subfamily rank. — Editor.) 



"Again, fertilization within the species is of every degree, and results therefore in simple penetration of sperm 

 which fails to make more than an early beginning of development or nothing at all, or it may give stages of change, 

 etc., up to blood formation, and from this point it may go on and stop after forming an embryo, or at any point 

 up to hatching; and when hatched, the fate is not yet settled; the bird may be deformed and still live; it may be too 

 weak to develop further or go on and die at three, four, five, six, or more days. All along the line we see that develop- 

 ment requires energy and stops or goes wrong for failure in this. Young birds often make failures. Doves reach 



the highest point at three to four years The energy of development and degree of fertility appear to be 



correlated." 



'Obtained by mating birds distantly related; "strength" is, in all probability, added by the act of crossing. — 

 Editor. 



