DEVELOPMENT AND PLACENTATION. 725 
“no larger than fern seed.” They are formed from germinal 
epithelium, the cells of which grow inwards in clustered 
masses into the connective tissue or stroma of the ovary. 
In each cluster one cell pre- 
dominates over its neigh- 
bours ; it becomes an ovum; 
the others invest and nourish 
it, and are called follicle cells. 
Tn the middle of each clump 
or Graafian follicle a cavity 
is formed containing fluid, 
and into this cavity the follicle 
cells immediately surrounding 
the ovum project, forming 
what is called the dzscus pro- 
ligerus (see Fig. 272, p. 514). 
When mature, the ovum 
protrudes on the surface of 
the ovary, and is liberated 
by the bursting of the Graafian 
follicle. Ovulation may occur 
spontaneously — as in man, 
monkeys, horse, cattle, pig, 
dogs; or after sexual union— 
as in rabbit, guinéa-pig, mouse, 
and cat. An ingrowth of 
epithelial cells surrounding 
the follicle develops into a 
glandular body called the 
corpus luteum. Its secretion 
is believed to be very import- 
ant—influencing the prepara- 
tion of the uterus, the early Hie Soy Berwenbaion wt 
nutrition of the embryo, and rabbit’s ovum.—After Van 
the multiplication of cells in Beneden. 
the milk glands. It seems 'e.¢., External cells (epiblast) ; z.c., 
that the ovary, besides produc- _iuternal cells (hypoblast); 2.2, 
ing ova, is a gland whose in- 
ternal secretion, passing into the blood, induces, directly or 
indirectly, the phenomena of heat and menstruation, and 
influences the uterus during pregnancy, 
ic 
