IMPREGNATION OF THE OVUM. 



Such aspiration of the seminal fluid by the uterus irritated to maximum 

 degree is by no means necessary to fecundation. The spermatozoa are capable 

 by their own movement of entering the uterus from the vaginal portion through 

 the clear mucus that normally occupies the cervical canal. ' Indeed, observations 

 as to impregnation without entrance of the penis, in consequence of pathological 

 obstructions, such as partial atresia of the vulva or vagina, show that spermatozoa 

 may traverse the entire vagina into the uterus. 



IMPREGNATION OF THE OVUM. 



The ovum is fecundated by the penetration of one spermatozoon. 



Since the time of Swammerdam (died 1685) it has been known that for fecunda- 

 tion to take place contact of the ovum with the seminal fluid is necessary and 

 indeed with the spermatozoa, which according to Hartsoecker penetrate into the 

 ovum. . Barry saw spermatozoa enter the interior of the rabbit's ovum. This 

 takes place with considerable rapidity by a boring-movement through the capsule 

 of the ovum. The invasion takes place eventually through pores that are present 

 or through the micropyle. 



In the mouse and some other mammals the ovary is surrounded by a space 

 filled with fluid (periovarial space) , to which both the ovum and the spermato- 

 zoon gain access; both are conveyed by aspirating movements of the tube into the 

 uterus. 



The viscid surface of the ovum affords a means for the attachment of the 

 spermatozoon. In the case of meroblastic ova the spermatozoon penetrates in 

 the situation of the nucleus; in that of holoblastic ova at the animal pole, when 

 this is present. At the spot where the head of the spermatozoon meets the yolk, 

 the latter throws out toward it a humplike elevation. As soon as a spermatozoon 

 has penetrated into the yolk, the entrance of other spermatozoa seems to be op- 

 posed by the appearance of a firm membrane the yolk-membrane upon its 

 surface, which, acting as a protecting wall, prevents the penetration of other 

 spermatozoa. Nevertheless in the case of meroblastic ova (selachians, reptiles, 

 insects and others) the penetration of several spermatozoa takes place normally 

 for the purpose of fecundation polyspermism. 



The place where fecundation (impregnation) takes place is either 

 the ovary (as indicated by the occurrence of abdominal pregnancy) or 

 the tube, whose numerous mucous folds constitute a suitable place of 

 lodgment for the spermatozoa. That fecundation may take place also 

 in the tube is shown by the occurrence of tubal gestation. Spermatozoa 

 must, accordingly, pass from the uterus through the tube to the ovary 

 and they do this probably by their own movement. Whether the per- 

 istaltic movements of the uterus and the tube assist in this transpor- 

 tation is uncertain. The ciliary movement of the tubal epithelium 

 can, however, have nothing to do with the phenomenon, as the movement 

 is directed outward. If the ovum enters the uterus unimpregnated, 

 it does not undergo fecundation here, as it perishes. It is believed 

 that the extruded ovum reaches the uterus within two or three weeks 

 (in dogs from eight to fourteen days). 



Double impregnation (twins) occurs once in 87 times (in tropical 

 regions more commonly); triplets once in 7600 times; quadruplets 

 once in 330,000 times; sextuplets are extremely rare; septuplets (?) 

 were born by Anna Breyers of Hamlin in 1600. The average number 

 of conceptions in women is 4^. The largest number of children observed 

 is from 32 to 38. 



By superfecundation is understood the occurrence of the impregnation of 

 two ova discharged at the same menstrual period, as a result of different copula- 

 tions. For example, a mare may throw a foal and a mule, after having been covered 

 first by a stallion and then by an ass. Thus, also, a woman has been observed to 

 give birth to a negro and a white twin. If, however, the second fecundation occurs 



