THE DEVELOPMENT OF THE UROGENITAL SYSTEM. 113 
vis in females alters in shape; not only do the generative organs 
themselves rapidly undergo increased development, but certain 
related glands (mamme) participate; hair appears in certain 
regions of the body; the larynx, especially in the male, under- 
goes enlargement and changes in the relative size of parts, re- 
sulting in an alteration of voice (breaking of the voice), etce.— 
all in conformity with that excess of nutritive energy which 
marks this biological epoch. 
Correlated with these physical changes are others belonging 
to the intellectual and moral (psychic) nature equally impor- 
tant, and, accordingly, the future being depends largely on the 
full and unwarped developments of these few years. 
Sexual maturity, or the capacity to furnish ripe sexual ele- 
ments (cells), is from the biological standpoint the most impor- 
tant result of the onset of that period termed, as regards the 
human species, puberty. 
The age at which this epoch is reached varies with race, 
sex, climate, and the moral influences which envelop the indi- 
vidual. In temperate regions and with European races pu- 
berty is reached at from about the thirteenth to the eighteenth 
year in the female, and rather later in the male, in whom de- 
velopment generally is somewhat slower. 
MENSTRUATION AND OVULATION. 
In all vertebrates, at periods recurring with great regu- 
larity, the generative organs of the female manifest unusual 
activity. This is characterized by increased vascularity of the 
_ ovary and adjacent parts; with other changes dependent on 
this, and that heightened nerve influence which, in the verte- 
brate, seems to be inseparable from all important functional 
changes. Ovulation is the maturation and discharge of ova 
from the Graafian follicles. The latter, reaching the exterior 
zone of the ovary, becoming distended and thinned, burst ex- 
ternally and thus free the ovum. The follicles being very vas- 
cular at this period, blood escapes, owing to this rupture, into 
the emptied capsule and clots; and as a result of organization 
and subsequent degeneration undergoes a certain series of 
changes dependent on the condition of the ovary and adjacent 
parts, which varies according as the ovum has been fertilized 
or not. When fertilization occurs the Graafian follicle under- 
goes changes of a more marked and lasting character, becom- 
ing a true corpus luteum of pregnancy. 
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