1884.] The Theory of Sex and Sexual Genesis. 789 
ty-nine cases, succeeded in producing at will such or such a sex” 
(Letourneau, Biology, p. 312). Experiments on the effect of late 
fertilization of the eggs of birds had previously been made by 
Knight, “ which,” he states, “to have been frequently repeated,” 
and which gave similar results. “ When the female was kept with- 
= out intercourse with the male up to nearly the time for laying, so 
_ that the eggs had advanced very far in their development at the 
. time of fertilization, the proportion of males among the offspring 
was very large, commonly about six out of seven” (Carpenter, 
_ peit, p. 979). 
= Inthe theoretical interpretation of these results, the important 
fact to be noted is, that the mature ovum, even without fertiliza- 
__ tion, generally undergoes segmentation in an imperfect manner 
__ before its death and dissolution takes place. Thus from the be- 
ginning of the period during which the ovum is capable of being 
_ impregnated to the time when segmentation begins, the proto- 
plasmic mass of the ovum undergoes a gradual change from a 
More stable to a less stable state of aggregation as a mass. This 
change is no doubt accelerated by .the access of the sperm-cell, 
at whatever time fertilization may take place. Still if fertilization 
takes place at a very early period, the interval of time which will 
follow before segmentation begins will be greater than it will 
when fertilization takes place at a later period. And there is evi- 
ice that during that interval the sperm-cell tends to become 
assimilated in its constitution to the germ-cell, and therefore, by 
hypothesis, to have its specific capacity or function of exciting 
cell-division to some extent weakened. Recent investigations 
_ fave shown that the act of impregnation consists in the forma- 
_ ton of a male “ pronucleus,” derived from the impregnating 
‘Perm-cell, which fuses with the female “ pronucleus” of the 
: -cell to constitute the single nucleus of the fertile ovum. 
i And Hertwig points out, “that considerable difference may be 
: in the occurrences which succeed impregnation, accord- 
: "Eto the relative period at which this takes place. When, in 
. 25; the impregnation is effected about an hour after the egg 
S laid, and previously to the formation of the polar-cells, the 
: Pronucleus appears at first to exert but little influence on 
eee Protoplasm, but after the formation of the second polar-cell 
‘he radial Strie around it become very marked, and the PSOR- 
"s rapidly grows in size. When it finally unites with the 
a oui = n a E A E a o a a 
> 
