324 



TEE POPULAR SCIENCE MONTHLY. 



constant average ratio between the sexes adapted to the conditions of 

 life, he gives his reasons for believing that this ratio is not determined 

 by any inner law, but by the influence of external conditions, which 

 act sometimes upon the parent organism, sometimes upon the egg be- 

 fore fertilization, sometimes upon the developing egg or embryo, and 

 sometimes, as in the case of many plants, upon the mature organism. 

 He also believes that the character of the influence thus exerted by 

 external conditions has been determined for the good of each species 

 — by natural selection. 



He treats, in the first part of his paper, of those conditions which 

 act upon the two parents in opposite ways, and he summarizes his 

 conclusions as follows : " Each species has acquired, through natural 

 selection, the useful property, in virtue of which any deviatio7i from 

 the average ratio between the sexes is corrected by an increased number 

 of births of the deficient sex, or a decreased number of births of the 

 sex which is in excess.''"' 



We have sj^ace for only two of the many illustrations which he 

 quotes to prove the existence of this law, and for further jDroof must 

 refer the reader to the long tables of statistics in the original paper. 



As the result of nearly a million observations of the birth of colts, 

 he shows that, as the number of mares put to a stallion in a year is in- 

 creased, there is a corresponding and regular increase in the number of 

 male colts as compared with the female colts, and he gives the follow- 

 ing summary : 



In three cases where the power of parthenogenetic reproduction 

 has been acquired as a compensation for the absence of males, the par- 

 thenogenetic eggs give rise either universally, or in the vast majority 

 of cases, to males. 



For instance, as bees destroy the males after they have been ren- 

 dered unnecessary by the fertilization of the queen, they are exposed 

 to the danger that when males are needed none may exist, and there 

 can be no doubt that the power of parthenogenetic reproduction has 

 been acquired by bees as a compensating adjustment. 



When the nuptial flight of the queen is delayed by accident, or 

 by the intervention of the breeder, the effect is, of course, equivalent 



