GERM-CELLS :—FERTILIZATION OF GERM. 559 
from other cells by the nature of their contents, though they are 
usually recognisable by the peculiar nuclei they present ; each 
cell is known as the germinal vesicle (fig. 302, d), whilst its 
nucleus (e) is designated the germinal spot.—The act of fertiliza- 
tien appears to consist in the contact of one or more spermato- 
zoids with the exterior of the germinal vesicle ; the sperma- 
tozoids, ceasing to move, undergo a sort of liquefaction ; and 
the product of their dissolution, being received by absorp- 
tion into the interior of the germinal vesicle, mingles with its 
contents, to form with them the basis of the new structure.— 
When, as usually happens, the germ-cells are developed in a 
Fig. 302.—Secrron or OvarRiuM oF Fow : 
a, fibrous substance of the ovary; by yolk; c, yolk-bag; d, germinal vesicle; e, 
germinal spot. 
special and distinct organ, this organ, which is termed the 
Ovary, has very commonly among the lower animals a glan- 
dular character, the mature ova being discharged by the ovi- 
duct, just as the products of secretion pass-off through the 
ducts of their respective glands: but among the Vertebrata 
the ovary has a much more solid texture, and the germ-cells, 
developed in the very midst of its fibrous tissue (fig. 302, a), 
have to find their way to its surface, and to burst forth from it ; 
being then received into an oviduct, whose trumpet-shaped 
‘mouth embraces the ovary, so as to prevent the liberated 
‘germs from falling (as they would otherwise do) into the 
Wisceral cavity of the body. 
733. With the “germ-cell” there is always associated in 
_Animals, as in Flowering Plants, a store of nutriment that 
sesrves for the early development of the germ ; this consists 
of a mixture of albuminous and oily matter, known as the - 
2yolk (fig. 302, 6); and it is inclosed in a membranous envelope ¢, 
