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378 DESIGN IN NATURE<br />
element actually entering into the female element. Not only does the ovum extrude part of its substance to make<br />
room for the male element, but an aperture, in many cases, is provided for the admission of the male element,<br />
which aperture is closed soon after this element has effected an entrance.<br />
Further, the male and female elements move towards each other both before and during impregnation. Thus,<br />
after coitus and before impregnation, the spermatozoon uses its vibratile, swimming tail on its way through the<br />
uterus to the Fallopian tube, and the movements of the cilia of the Fallopian tube assist the ovum in its passage<br />
through it ; the junction of the male and female elements and impregnation usually taking place in the tube. In<br />
the process of impregnation the male and female elements move still more closely together, and carry out in the<br />
fullest sense the original purpose of a perfect union. That the male and female elements should be produced in<br />
two separate individuals and independently, and after the congress of the sexes should seek each other and travel<br />
long distances to effect a union, is at once a fundamental and striking fact in physiology, and plamly proclaims<br />
pre-arrangement and design.<br />
in both the male and female elements ;<br />
Reproduction consists of a progressive series of co-ordinated movements and changes<br />
the spermatozoon even shedding its vibratile tail when it enters the ovum<br />
and the tail is no longer required. The changes to which allusion has been made take place before the division or<br />
segmentation of the ovum occurs. There are in reality two sets of changes to be considered, namely, (a) changes<br />
occurring during impregnation and before segmentation of the ovum takes place ; and (b) changes which occur after<br />
segmentation or division of the ovum. It is necessary to say a few words regarding each, as the impregnation and<br />
development of the ovum afford some of the best illustrations of design known to anatomy, physiology, and biology.<br />
§ 73. Ripening of the Ovum :<br />
Formation of Polar Globules.<br />
Either before or soon after the ovum escapes from the Graafian folUcle of the ovary it undergoes a pecuhar<br />
change, consisting of unequal cell-division or germination, and the extrusion from its vitellus of two minute spherical<br />
bodies, the so-called polar globules or directive corpuscles (Plate Ixxxvi., G to N, inclusive). The change in<br />
question is independent of, but connected with, fertilisation, and is most important, as fertilisation does not occur<br />
without it. The cell division and extrusion of polar globules are almost universal in animals. They occur also<br />
in plants, and have therefore much significance. The polar globules (directive corpuscles) determine the pole at<br />
which the fijst segmentation mil occur in the fertihsed ovum. The globules consist of two small portions of the<br />
nucleus of the ovum, plus a certain amount of protoplasm. When they are to be extruded the germinal vesicle<br />
seeks the surface of the vitellus and rmdergoes changes indicative of a nucleus about to divide. It also loses its<br />
pecuhar outhne and shape. The vesicle, as a matter of fact, divides into two ; the one portion being extruded into<br />
the perivitelUne space, the other being retained in the vitellus to be extruded subsequently.<br />
The remains of the germinal vesicle, designated the female pronucleus, now leaves the surface of the vitellus and<br />
seeks the centre, where it awaits the arrival of the male element (spermatozoon) ; the latter, when fertilisation takes<br />
place, forming the male pronucleus.<br />
The junction of the male and female pronuclei results in the formation of a new nucleus, and ultimately,<br />
a new being. It happens occasionally that the ovum receives a spermatozoon before it extrudes its polar<br />
globules.<br />
According to Minot " every cell which results from the division of a fertilised ovum is hermaphrodite." He<br />
also beUeved that the descendants of every such cell are also hermaphrodite. He founded his beUef on the duality<br />
of the fertilised ovum, this containing male and female elements. Weismann in his theory of heredity propounded<br />
a somewhat different view. In his opinion " every animal and vegetable cell contains two kinds of hving matter,<br />
namely, nuclear plasma and nutritive plasma : the former endowed with germinative, directing, and hereditary func-<br />
tions ; the latter with the assimilation of food and the more purely physical functions, such as contraction, nerve-<br />
conduction, secretion, &c." The nuclear plasma, according to Weismann, controls the functions discharged by the<br />
nutritive plasma. Weismann went further and divided the nuclear plasma into germinal plasma and histogenetic<br />
plasma. To the former he assigned primitive form and periodicity ; to the latter the division, growth, and differentia-<br />
tion of the cell. As fertihsation impUes the addition to the ovum of a certain amount of male germinal matter,<br />
Weismann assumed that the ovum, prior to fertihsation and development, must get rid of its histogenetic plasma<br />
and a proportion of germinal plasma equal in amount to that brought to it by the spermatozoon. This adjustment<br />
is arrived at by the extrusion (a) of one (histogenetic) polar globule, and (b) of the other (germinal) globule. By<br />
this arrangement a certain amount of the primitive or germinal plasma of the original ovum always remains, and<br />
in due course transmits the accumulated ancestral peculiarities of both parents. Heredity is essentially molecular<br />
in its nature. It is to molecules and the atoms forming them that questions of heredity and affinity must ultimately<br />
be referred. Atoms and molecules precede all cell formation and division.