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 



Fig. 5. — ^The human egg a hundred times en. 

 larged. a. The kernel speck, or nucleolus (the 

 so-called germinal spot of the egg), h. 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 

 efjofs of other mammals are of the same form. 



-'00" 



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 (b), 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 



