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DESIGN IN THE REPRODUCTION AND GROWTH OF ANIMALS 375
The production of the male and female elements in the mammal is an elaborate process, and begins at an early
age, even prior to puberty. The testes of the male and the ovaries of the female supply the spermatozoa and ova
respectively. The spermatozoa or male elements, when puberty is attained, are always available ; the ova or female
element being only available monthly or after each menstrual period. The spermatozoa are furnished in incredible
numbers, the ova in small numbers, generally one or two, but sometimes three, four, or more. The number of the
offspring corresponds with the number of impregnated ova which occupy the uterus. Single births are most
common, but twins and triplets are by no means rare.
The manner in which the ova are produced and find their way into the uterus is at once interesting and
instructive.
The ovaries, two in number, are situated near the fundus of the uterus, of which they may be said to form
appendages, although they are altogether distinct from it. They exist in the female child, and as puberty approaches
the ova which they contain begin to ripen. When puberty is attained the ripe ova—one, two, or more—are dis-
charged monthly from the surfaces of the ovaries and caught by the funnel-shaped, fimbriated extremities of the
Fallopian tubes in a very special and remarkable way, and conveyed by them to the interior of the uterus. The
Fallopian tubes with their fimbriated extremities are not structurally attached to the ovaries, but by a series of vital
and most extraordinary movements they sweep over the surface of the ovaries so effectually that they almost
invariably succeed in catching the ripe ova on their being discharged. By some refined and totally inexplicable
affinity they feel about for the ripe ova, and, having located them, temporarily attach themselves to the portion
of the ovaries about to erupt or discharge. The movements of the Fallopian tubes are essentially vital in character.
They are spontaneous and independent, and are not caused by any inherent irritability or extraneous stimulation.
The Fallopian tubes are special fundamental structures, and perform a most important fimction in the reproduction
of mammals. If they fail to catch and convey the ovum or ova to the uterus, extra-uterine gestation, that is, gesta-
tion in the Fallopian tubes, or abdominal cavity, occurs, which sooner or later endangers the Ufe of the mother, and
necessitates the performance of the Caesarian operation or section.
Gestation and development usually occur in the uterus, but, as indicated, they may occur in the Fallopian tubes,
or even on the surface of the ovaries, giving rise to Fallopian tube or extra-uterine pregnancy—both requiring
operation. Seeing the impregnated ovum or ova can Hve and develop outside the uterus, and on what are practi-
cally living, serous surfaces which merely furnish heat and moisture, it follows that quickened ova are to be regarded
as parasites, that is, living things growing upon living things, as happens in mistletoe growing upon apple or other
trees. I first directed attention to the parasitic nature of the developing human ova in 1872,^ and more extended
observation and experiment confirm me in this view. The view, I am glad to be able to state, has found general
acceptance.
The impregnated human ovum contains in its substance the pabulum required to nourish it until it has found
a suitable niche in the mucous lining of the uterus. Once there it adheres by simple apposition. At the outset,
and until the shaggy chorion is formed, it is fed by osmotic currents consisting mainly of liquor sanguinis exuded
from the blood-vessels of the mother. When the shaggy chorion is formed, the ovum throws out thread-Uke pro-
cesses {villi) which increase the osmotic surface. Later, the ovum develops blood-vessels and capillaries ; the latter
interdigitating and passing between similar capillaries found in the mucous lining of the uterus of the mother. In
this way osmotic exchange is still further increased. The ovum in the later stages of development also obtains
nourishment from uterine glandular secretions. The interchange of fluids and gases between the foetus and the
mother is carried on by the placenta, which is composed of a foetal and a material portion ; the two portions very
closely resembling each other structurally.
The maternal portion of the placenta consists of the thickened mucous Uning of the uterus, of glands, lymphatics,
nerves, capillary, and other blood-vessels. It at once forms a stomach and a lung for the foetus, as it provides the
serum of aerated blood and nutritive gland products. The foetal portion of the placenta consists, for the most part,
of connective tissue and of capillary and other blood-vessels. The maternal and foetal portions of the placenta are
bounded by epitheUum, and as they are merely placed in apposition with fluids and gases on either side the
epithelium, a free interchange of nutritive and waste products, fluid and gaseous, takes place as between the parent
and offspring. As the foetus is only temporarily grafted on the parent by a loose uterine arrangement, it follows
that at the full term the foetus is expelled by rhythmic uterine contractions which induce the so-called labour-pains.
When the child is born the foetal portion of the placenta known as the after-birth is separated from the maternal
portion by uterine contractions, and by a vital process resembhng that by which the leaf is separated from the
branch in autumn.
In healthy natural labours there is next to no laceration of blood-vessels, either maternal or foetal, and conse-
• "Physiology of the Circulation in Plants, in the Lower Animals, and in Man." Edinhurtjh Medical Juunial, 1872-73.