298 THE HISTORY OF CREATION. 
or yolk-membrane, which here bears the special name of 
zona pellucida (d). The eggs of many lower animals 
(for example of many Medusze) differ from this in being 
naked cells, as the outer covering, or cell-membrane, is 
wanting. 
As soon as the egg (ovulum) of the mammal has attained 
its full maturity, it leaves the ovary of the female, in which 
it originates, and passes into the oviduct, and through this 
narrow passage into the wider pouch or womb (uterus). If, 
meanwhile, the egg is fructified by the male seed (sperm), it 
develops itself in this pouch into an embryo, and does not 
leave it until perfectly developed and capable of coming 
into the world at birth as a young mammal. 
The variations of form and transformations which the 
fructified egg must go through within the uterus before it 
assumes the form of the mammal are exceedingly remark- 
able, and proceed from the beginning in man, in precisely 
the same way as in the other mammals. At first the fructi- 
fied egg of the mammal acts as a single-celled organism, 
which is about to propagate independently and increase 
itself; for example, an Amceba (compare Fig. 2, p. 188). 
In point of fact the simple egg-cell becomes two, by the 
process of cell-division which I have previously described. 
There arise from the single germinal spot (the small kernel- 
speck of the original simple egg-cell) two new kernel-specks, 
and then in like manner, out of the germinal vesicle (the 
nucleus), two new cell-kernels. Then, and not until then, 
does the globular protoplasma first separate itself by an 
equatorial furrow into two halves, in such a manner that 
each half encloses one of the two kernels, together with 
its kernel-speck. Thus the simple egg-cell, within the 
