STEIULITV. 65 



noted here. The germinal spot, })reviously at the inner surface, passes 

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

 the surface, goes to the centre of the yolk or vitellns ; while the mem- 

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

 the ovum is discharged, the tunica (jraiiulosa and rctinacnla accompany 

 it through the small opening in the vesicle ; the whole being received 

 into the pavilion or infundibulum of the Fallopian tube, which at this 

 time is tirndy applied against the ovary. 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 nmcous membrane lining this duct, until at last it reaches the 

 uterus. 



CHAPTER III. 

 Sterility. 



Hitherto we have been treating of fecundation as if it were always 

 a sure result of the coupling of the male and feniale sexes at a 

 certain period. Successful fecundation, however, is not always the case, 

 and in some species — particularly the Equine — sterility, temporary or 

 permanent, in the female is far from being uncommon, and is some- 

 times serious. Sterility, barrenness, or infecundity depends on numerous 

 causes, to some of which we must allude, as in distinguishing their 

 presence we may be able to remove or counteract them. 



It is difhcult to ascertain the extent to which it prevails, especially in 

 the larger and more important animals. In the Stud Book, it is shown 

 that among thoroughbred Mares the percentage of those which carry 

 foal is 73"8G, and those which abort or are infecund 26"64. In the 

 studs of France the fruitful Mares are o9-o7, and the unfruitful ones 

 4043 per cent. The Due de Guiche gives 68 per cent, of fecund 

 Mares. At the haras of Pin, during a period of twenty years, there 

 was a percentage of 68- 27 fecund Mares, abortions 5-06, non-fecund 

 26G7 ; while at the Pompadour haras, where Oriental horses were 

 chieHy bred, the births in three years were 79'55, abortions 2*27, and 

 non-fecunds 2045. 



In the Cow, the fecundations appear to average about 79 per cent. 



With the Sheep, sterility or infecundity is not so common. RuefT, at 

 Hohenheim, found among 8,500 sheep, only 740, or 8 per cent., unfruitful. 



Sterility may depend upon organic or pliysical causes, and may 

 amount to permanent impotence, more particularly when congenital 

 and located in the generative apparatus. Monstrosities, hermaphro- 

 dites, animals in which one or more important organs of the sexual 

 apparatus are absent, and hybrids, are generally permanently sterile.' 



Prolonged continence and old age are not infrequent causes of in- 

 fecundity, as is witnessed in Mares which liave worked for many years 

 in towns, and then been transferred for breeding purposes. 



Change of climate has in many cases a marked influence on fecundity 

 — sometimes putting it altogether in abeyance, and at others rendering 

 the animals infecund for only a longer or shorter period. It may also 

 be impaired, or suspended ten)porarily or permanently, by abuse of 

 the generative functions, bad hygiene, etc. 



' There are exceptions to this rule. Several well authenticated instancea are recorded 

 in which the suliped mule haa bred, as well aa other hybrids. 



5 



