246 BREEDING 



IMPREGNATION 



Impregnation is effected by the contact of the sperm -cell of the male 

 with the germ-cell of the female. The precise manner of the contact, and 

 the means employed to ensure it, are of no consequence to the result. In 

 the most highly organized mammals, for instance, the fluid secreted by the 

 testicles of the male (semen), with fluid from the prostate and other glands, 

 is conveyed to the generative organs of the female by means of the intro- 

 mittent organ, which injects it forcibly into the vagina, and to some extent 

 also through the open mouth of the uterus into that organ. Sperm-cells, 

 or, as they may more correctly be termed, spermatozoa, which have been 

 set free from tlie sperm-cells, are abundant in the fluid so injected. These 

 actively moving bodies are the essential agents in impregnation, and 

 whether they reach the germ-cells of the ovum in the natural way, or are 

 conveyed artificially by instrumental means, as in artificial insemination, 

 the effect of their contact is tlie same. The previously passive germ-cell 

 becomes active under the action of the stimulus imparted by the sperm-cell, 

 which rouses the developmental force, before lying dormant, in the ger- 

 minal vesicle of the ovum. 



Another important factor in the generative function — the receptive con- 

 dition of the ovum — is at this stage to be considered. Not every contact 

 between the sperm and the germ is fruitful; possibly the power of the 

 sperm-cell may always be active, but it is quite certain that the ova in the 

 ovarium are not at all times ready to react to the mysterious force which 

 the sperm-cell is ready to transmit. 



During the period of life which includes the power of procreation, 

 development of ova is always going on in the substance of the ovary. From 

 a mere speck of germinal matter or protoplasm, the egg originates as a 

 simple cell, gradually attaining to the condition of the mature ovum with its 

 external vitelline membrane {zona pellucida), the yolk-sac containing the 

 yolk and a germinal vesicle with the central germinal spot. As the 

 development of the ovum reaches nearer to the point of perfection, the 

 Graafian follicle in which it is contained and protected, advances to the 

 surface of the ovarium, blood circulation in the external membranes in- 

 creases in volume and rapidity, and soon the surface of the Graafian follicle 

 is covered with an arboresque arrangement of brightly coloured vessels. In 

 due time the follicle bursts and sets the mature ovum free to pass into the 

 open fimbriated mouth of the Fallopian tube, through which it passes to the 

 interior of the uterus. If no contact takes place with the sperm-cell, the 

 ovum, although readv to receive the stimulus, which, however, may not be 



