THE HUMAN EGG. 297 
exist between the eggs of different mammals and that of 
‘man do not consist in the form, but in the chemical mixture, 
in the molecular composition of the albuminous combination 
of carbon, of which the egg essentially consists. These 
minute individual differences of all eggs, which depend upon 
indirect or potential adaptation (and especially upon the 
law of individual adaptation), are indeed not directly per- 
ceptible to the exceedingly imperfect senses of man, but are 
cognisable through indirect means, as the primary causes of 
the difference of all individuals. 
The human egg is, like that of all other mammals, a 
small globular bladder, which contains all the constituent 
parts of a simple organic cell (Fig. 5). The most essential 
Fic. 5.—The human egg a hundred times en- 
larged. a. The kernel speck,or nucleolus (the 
so-called germinal spot of the egg). b. Kernel, 
or nucleus (the so-called germinal vesicle of the 
egg). c.Cell-substance, or protoplasm (so-called 
yolk of the egg). d. Cell-membrane (the yolk- 
membrane of the egg; in mammals, on account 
of its transparency, called zona pellucida). The 
P eges of other mammals are of the same form. 
parts of it are the mucous cell-substance, or the protoplasma 
(c), which in an egg is called the “ yolk,” and the cell-kernel, 
or nucleus (6), surrounded by it, which is here called by the 
special name of the “germinal vesicle.” The latter is a deli- 
cate, clear, glassy globule of albumen, of about 1-600th part of 
an inch in diameter, and surrounds a still smaller, sharply- 
marked, rounded granule (a), the kernel-speck, or the nucle- 
olus of the cell (in the egg it is called the “ germinal spot”). 
The outside of the globular egg-cell of a mammal is sur- 
rounded by a thick pellucid membrane, the cell-membrane 
