FECUNDATION. 6i 



Sheep, having usually only one offspring at a time, only one vesicle ripens 

 during oestrum ; the Goat has most frequently two young, and in this case 

 a vesicle ruptures in each ovary ; while the Pig and Carnivora having 

 several at a birth, a corresponding number of vesicles open and their 

 contents occupy each cornu of the uterus. 



The ovum liberated by the bursting of the vesicle is seized by the pavil- 

 ion of the oviduct, which is applied somewhat closely to the surface of the 

 organ, and is carried down the tube to the uterus, where, if fecundation 

 does not ensue, it remains only a brief period before it is expelled or 

 perishes. The seizure of the ovum, as has been stated, is all the more 

 certain in proportion, as the pavilion is large enough to grasp a large 

 surface of the ovary : this condition is found most developed in the 

 Carnivora. 



CHAPTER II. 

 Fecundation. 



The effective intercourse of the male with the female is followed by cer- 

 tain remarkable changes in the ovum and generative apparatus of the 

 latter, which, at first known as fecundation, conception, or impregnation^ 

 ultimately results in the formation of a new creature possessed, to a cer- 

 tain degree, of individual or independent life. The intercourse, to be 

 effective, depends upon the presence of a healthy ovum in the apparatus 

 of the female, and the introduction into this apparatus of the seminal 

 fluid by the special organ of the male. This fluid contains the essential 

 elements known as " spermatozoa " — organic particles of a particular 

 shape, and endowed with motion. For conception, it is absolutely neces- 

 sary that the ovum of the female should be brought into contact with 

 these particles ; though whether this contact can occur in the ovisac, 

 prior to its escape, has not yet been definitely ascertained. It is certain 

 that by reason of their particular movements, and also doubtless through 

 the aid they receive from the special motion of the ciliated epithelium 

 covering certain portions of the lining membrane of the uterus, these 

 spermatozoa, when the uterine opening is patent, are diffused soon after 

 coitus to the most distant parts of that cavity, and high up in the Fallopian 

 tubes ; though they have never been traced so far as the ovisac. Never- 

 theless, a very strong argument in favor of their attaining this region, 

 and producing what is called " ovarian " or " tubal impregnation," is 

 afforded in the occurrence of extra-uterine — ovarian or tubal — gestation -, 

 for in this case the spermatozoa must have reached both oviduct and ovary. 

 Before the ovum leaves the ovary, changes occur in it which may be 

 noted here. The germinal spot, previously at the inner surface, passes to 

 the centre of the germinal vesicles ; and this, which was before at the 

 surface, goes to the centre of the yolk or vitellus ; while the membrane 

 investing the latter, from being thin, suddenly thickens. When the ovum 

 is discharged, the tunica granulosa and retinacu/a accompany it through 

 the small opening in the visicle ; the whole being received into the pavilion 

 or infundibulum of the Fallopian tube, which at this time is firmly applied 

 against the ovar}'. Arrived at this part, the ovum is carried along by the 

 slow vermicular motion or contraction of the tube, as well as by the ciliary 

 movement of the cells covering the mucous membrane lining this duct 

 until at last it reaches the uterus. 



