THE DEVELOPMENT OF THE UROGENITAL SYSTEM. 115 
parts of the mucous lining of the uterus undergo softening 
and fatty degeneration, they are thrown off and renewed at 
these periods (catamenia, menses, etc.), provided pregnancy 
does not take place. In mammals below man, in their nat- 
ural state, pregnancy does almost invariably take place at 
such times, hence this exalted activity of the mucous coat of 
the uterus, in preparation for the reception and nutrition of 
the ovum, is not often in vain. In the human subject the 
menses appear monthly; pregnancy may or may not occur, and 
consequently there may be waste of nature’s forces; though 
there is a certain amount of evidence that menstruation does 
not wholly represent a loss; but that it is largely of that char- 
acter among a certain class of women is only too evident. As 
can be readily understood, the catamenial flow may take place 
prior to, during, or after the rupture of the egg-capsule. 
As the uterus is well supplied with glands, during this 
period of increased functional activity of its lining membrane, 
mucus in considerable excess over the usual quantity is dis- 
charged; and this phase of activity is continued should preg- 
nancy occur. 
All the parts of the generative organs are supplied with 
muscular tissue, and with nerves as well as blood-vessels, so 
that it is possible to understand how, by the influence of nerve- 
centers, the various events of ovulation, menstruation, and 
those that follow when pregnancy takes place, form a related 
series, very regular in their succession, though little prominent 
in the consciousness of the individual animal when normal. 
THE NUTRITION OF THE OvUM (OOSPERM). 
This will be best understood if it be remembered that the 
ovum is a cell, undifferentiated in most directions, and thus a 
sort of amesboid organism. In the fowl it is known that the 
cells of the primitive germ devour, amceba-like, the yelk-cells, 
while in the mammalian oviduct the ovum is surrounded by 
abundance of proteid, which is doubtless utilized in a somewhat 
similar fashion, as also in the uterus itself, until the embryonic 
membranes have formed. To speak of the ovum being nour- 
ished by diffusion, and especially by osmosis, is an unnecessary 
assumption, and, as we believe, at variance with fundamental 
‘principles; for we doubt much whether any vital process is 
one of pure osmosis. As soon as the yelk-sac and allantois 
have been formed, nutriment is derived in great part through 
