646 STRUCTURE AND GROWTH OF DOMESTICATED ANIMALS. 
as one of the full-grown yolks drops, to be taken up by the fal- 
lopian tubes and carried through the oviduct, there to be sur- 
rounded by albumen, and then by a shell, — another grows larger, 
and when all those which are at any moment of full size have 
been laid, they are followed by another crop, and crop after crop 
comes to the surface of the organ, ready to be laid in succession. 
If you watch their growth, it is easy to see that each one passes 
into the condition of the eggs higher in size by a process of in- 
crease which is similar to the process by which a young animal 
grows to acquire the dimensions of an adult. Nobody now doubts 
that these small granules scattered through the ovary are really 
eggs in their incipient condition. 
How do they look when examined under the microscope,—say 
under a microscope magnifying two hundred and fifty times the - 
diameter,—an egg, therefore, which could not be seen by any 
human eye? You magnify it, as I have said, two hundred and 
fifty times, and you will see that that egg is a sphere, which you 
may, with the microscope, magnify to look as large as a full- 
grown yolk. It is then perfectly transparent, as if it were full of 
a uniform fluid, like water; but at some places on the side it has 
a little vesicle. a little bag, which is also transparent, and may 
only be seen under skilful management ; in this again there is still 
another microscopic body which appears like a small dot. Now 
you examine an egg a little larger than that, and you will perceive 
that in it the fluid mass is obscured slightly by small dots. If you 
apply the highest powers of the microscope to these dots, you very 
soon find that they are not solid granules, but that they are hollow 
vesicles which, in their turn, produce other granules within them- 
selves, so that the growth of an egg is in fact the enlargement of 
little granule-like masses of animal substance, which are trans- 
formed into bag-like bodies within which the same process is re- 
peated over and over again. As the whole egg grows larger, these 
little granules burst and scatter their contents into the surrounding 
fluid; and the egg, from perfectly white, becomes slightly tinged 
with yellow, and finally grows more and more opaque; and, when 
the yolk has acquired its full size and is ready to drop, it is 
really an opaque mass, but consisting throughout of these minute 
granules. 
Now let us take the ovary of the rabbit, the guinea-pig, or any 
ruped, and examine its contents, and we see eggs ex- 
