378 DESIGN IN NATURE 



element actually entering into the female element. Not only does the ovum extrude part of its substance to make 

 room for the male element, but an aperture, in many cases, is provided for the admission of the male element, 

 which aperture is closed soon after this element has effected an entrance. 



Further, the male and female elements move towards each other both before and during impregnation. Thus, 

 after coitus and before impregnation, the spermatozoon uses its vibratile, swimming tail on its way through the 

 uterus to the Fallopian tube, and the movements of the cilia of the Fallopian tube assist the ovum in its passage 

 through it ; the junction of the male and female elements and impregnation usually taking place in the tube. In 

 the process of impregnation the male and female elements move still more closely together, and carry out in the 

 fullest sense the original purpose of a perfect union. That the male and female elements should be produced in 

 two separate individuals and independently, and after the congress of the sexes should seek each other and travel 

 long distances to effect a union, is at once a fundamental and striking fact in physiology, and plamly proclaims 

 pre-arrangement and design. Reproduction consists of a progressive series of co-ordinated movements and changes 

 in both the male and female elements ; the spermatozoon even shedding its vibratile tail when it enters the ovum 

 and the tail is no longer required. The changes to which allusion has been made take place before the division or 

 segmentation of the ovum occurs. There are in reality two sets of changes to be considered, namely, (a) changes 

 occurring during impregnation and before segmentation of the ovum takes place ; and (b) changes which occur after 

 segmentation or division of the ovum. It is necessary to say a few words regarding each, as the impregnation and 

 development of the ovum afford some of the best illustrations of design known to anatomy, physiology, and biology. 



§ 73. Ripening of the Ovum : Formation of Polar Globules. 



Either before or soon after the ovum escapes from the Graafian folUcle of the ovary it undergoes a pecuhar 

 change, consisting of unequal cell-division or germination, and the extrusion from its vitellus of two minute spherical 

 bodies, the so-called polar globules or directive corpuscles (Plate Ixxxvi., G to N, inclusive). The change in 

 question is independent of, but connected with, fertilisation, and is most important, as fertilisation does not occur 

 without it. The cell division and extrusion of polar globules are almost universal in animals. They occur also 

 in plants, and have therefore much significance. The polar globules (directive corpuscles) determine the pole at 

 which the fijst segmentation mil occur in the fertihsed ovum. The globules consist of two small portions of the 

 nucleus of the ovum, plus a certain amount of protoplasm. When they are to be extruded the germinal vesicle 

 seeks the surface of the vitellus and rmdergoes changes indicative of a nucleus about to divide. It also loses its 

 pecuhar outhne and shape. The vesicle, as a matter of fact, divides into two ; the one portion being extruded into 

 the perivitelUne space, the other being retained in the vitellus to be extruded subsequently. 



The remains of the germinal vesicle, designated the female pronucleus, now leaves the surface of the vitellus and 

 seeks the centre, where it awaits the arrival of the male element (spermatozoon) ; the latter, when fertilisation takes 

 place, forming the male pronucleus. 



The junction of the male and female pronuclei results in the formation of a new nucleus, and ultimately, 

 a new being. It happens occasionally that the ovum receives a spermatozoon before it extrudes its polar 

 globules. 



According to Minot " every cell which results from the division of a fertilised ovum is hermaphrodite." He 

 also beUeved that the descendants of every such cell are also hermaphrodite. He founded his beUef on the duality 

 of the fertilised ovum, this containing male and female elements. Weismann in his theory of heredity propounded 

 a somewhat different view. In his opinion " every animal and vegetable cell contains two kinds of hving matter, 

 namely, nuclear plasma and nutritive plasma : the former endowed with germinative, directing, and hereditary func- 

 tions ; the latter with the assimilation of food and the more purely physical functions, such as contraction, nerve- 

 conduction, secretion, &c." The nuclear plasma, according to Weismann, controls the functions discharged by the 

 nutritive plasma. Weismann went further and divided the nuclear plasma into germinal plasma and histogenetic 

 plasma. To the former he assigned primitive form and periodicity ; to the latter the division, growth, and differentia- 

 tion of the cell. As fertihsation impUes the addition to the ovum of a certain amount of male germinal matter, 

 Weismann assumed that the ovum, prior to fertihsation and development, must get rid of its histogenetic plasma 

 and a proportion of germinal plasma equal in amount to that brought to it by the spermatozoon. This adjustment 

 is arrived at by the extrusion (a) of one (histogenetic) polar globule, and (b) of the other (germinal) globule. By 

 this arrangement a certain amount of the primitive or germinal plasma of the original ovum always remains, and 

 in due course transmits the accumulated ancestral peculiarities of both parents. Heredity is essentially molecular 

 in its nature. It is to molecules and the atoms forming them that questions of heredity and affinity must ultimately 

 be referred. Atoms and molecules precede all cell formation and division. 



