REPRODUCTION, 5T 
by a movement imparted to it by the muscular walls of the 
latter, similar to that of the gullet during the swallowing of 
food; that this tube is provided with glands which secrete in 
turn the albumen, the membrane (outer), the lime salts of the 
shell, etc. *The twisted appearance of the rope-like structures 
(chalaze) at each end is owing to the spiral rotatory movement 
the egg has undergone in its descent. 
The air-chamber at the larger end is not present from the 
first, but results from evaporation of the fluids of the albumen 
and the entrance of atmospheric air after the egg is laid some 
time. 
THE ORIGIN AND DEVELOPMENT OF THE OvuM. 
Between that protrusion of cells which gives rise to the 
bud which develops directly into the new individual, and that 
which forms the ovary with- 
in which the ovum as a mod- 
ified cell arises, there is not 
in Hydra much difference at 
first to be observed. 
In the mammal, however, 
the ovary is a more complex 
structure, though, relatively 
to many organs, still simple. 
It consists, in the main, of 
connective tissue supplied 
with vessels and nerves in- 
closing modifications of that 
tissue (Graafian follicles) 
within which the ovum is 
matured. The ovum and the : : 
. a i Fie. 61.—Section through portion of the ovary 
follicles arise from an inver- of mammal, illustrating mode of develop- 
. 3 a ment of the Graafian follicles (Wieder- 
sion of epithelial cells, on a _ sheim). D, discus proligerus ; Zi, ripe ovum ; 
a O G, follicular cells of germinal epithelium ; 
portion of the body cavity g, blood-vessels ; K, germinal vesicle (nucle- 
e . . ‘ us)and germinal spot (nucleolus): KE, ger- 
(germinal ridge), which give minal epithelium ; Ly, liquor follieult ; Mg, 
. : b tuni . i 
rise to the ovum itself, and —@pithelum ?'Mp, zona. pellucida : PS, in 
G wths from the germinal epithelium, ova- 
the other cells surrounding — flan tubes by means of whic , some of the 
it in the Graafian follicle. Hum 8; cavity which appears eithisy the 
. . Graafian follicle ; So, stroma of ov: 3 Th 
At first these inversions form iheen folliculi or teneule : "e, primitive oe 
] ; When an ovum with its surrounding cells 
tubules (eg g-tubes) which lat- has become separated from the eo it is 
er become broken up into iso- known as a Graafian follicle. 
lated nests of cells, the fore-runners of the Graafian follicles. 
The Graafian follicle consists externally of a fibrous capsule 
