REPRODUCTION IN THE HIGHER ANIMALS 1119 



middle piece originally containing the male centrosome and attrac- 

 tion sphere, p. 5) which is the essential contribution of the male to the 

 reproductive process. The tail of the spermatozoon is simply, from 

 the physiological point of view, a motile arrangement, whose function 

 it is to carry the nucleus of the male element, freighted with all that 

 the father can transmit to the offspring, into the neighbourhood of 

 the female reproductive element or ovum. After the spermatozoon 

 has penetrated the ovum its tail disappears, being probably 

 absorbed. The function of the accessory reproductive glands, the 

 prostate, the seminal vesicles, and Cowper's gland, are not well 

 understood. But the spermatozoa in the act of ejaculation are 

 mixed with the secretions of these glands, and therefore it is to be 

 supposed that they are of importance. When the prostate and the 

 seminal vesicles are removed in white rats, the female is no longer 

 fertilized, although the sexual power of the male is unaltered. The 

 testes apparently develop spermatozoa in the normal manner, but 

 for some reason they either do reach the ovum or do not react 

 with it normally if they do reach it. When the testes are re- 

 moved from a young animal, the development of the prostate is 

 interfered with; in an adult animal the gland atrophies. 



The ovum also begins as a typical cell with nucleus (germinal 

 vesicle), nucleolus (germinal spot), centrosome and attraction sphere, 

 and it forms, by its repeated subdivision, all the cells of the fcetal 

 body. But, except in some (parthenogenetio) forms, it never 

 awakens to this reproductive activity till fecundation has occurred; 

 and fecundation essentially consists in the union of the mab with the 

 female element, or rather in the union of the male and female nuclei. 



From time to time a ripe Graafian follicle, overdistended by its 

 liquor folliculi, bursts on the surface of the ovary and discharges an 

 ovum. It is probable that in the majority of mammals (e.g., the 

 cow, mare, sow, sheep, and bitch) ovulation, or the discharge of 

 the ovum, occurs spontaneously during oestrus (period of heat). 

 In others (e.g., the rabbit, ferret, and cat), it seems only to take place 

 as a result of copulation. Whether sexual intercourse has any in- 

 fluence upon ovulation in women can hardly be considered as settled. 

 The common opinion is that most ova are discharged spontaneously 

 at the time of the menstrual period, but some writers take the view 

 that the discharge bears no relation to menstruation. Only one 

 ovum seems to be shed each month. It was foimerly believed that 

 the frayed or fimbriated end of the Fallopian tube, rising up finger- 

 like from the dilatation of its bloodvessels, grasps the ovum. But 

 it is more than doubtful whether this occurs. It is more probable 

 that the ovum is first discharged into the pelvic cavity, and 

 is guided to the orifice of the Fallopian tube, not necessarily 

 that of its own side, by the movements of the cilia around the 

 orifice, and then passed slowly along the tube by the downward 



