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the alkaline mucus, which increases the activity of their movements, 

 may pass through the uterus into the Fallopian tubes, and even to the 

 surface of the ovaries. Precisely how their passage is effected, it is 

 difficult to say. It can be attributed only to the movements of the sper- 

 matozoids themselves, to capillary action, and to a possible peristaltic con- 

 traction of the muscular structures ; but these points have not as yet been 

 subjects of positive demonstration. As regards the human female, it is 

 impossible to give a definite idea of the time required for the passage of 

 the spermatozoids to the ovaries or for the descent of the ovum into the 

 uterus ; and it is readily understood how these questions hardly admit of 

 experimental investigation. It is known, however, that spermatozoids 

 reach the ovaries, and they have been seen in motion on their surface, 

 seven or eight days after connection. 



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The ordinary situation at which the ovum is fertilized is the 

 dilated, or external portion of the Fallopian tube. All authorities are 

 agreed that fertilization does not take place in the cavity of the uterus. 

 In rabbits, when the ovum has descended into the uterus, it is sur- 

 rounded with a dense albuminous coating which the spermatozoids can 

 not penetrate. It is possible that this occurs in the human subject. 

 Cases of abdominal pregnancy show that an ovum may be fertilized 

 on the ovary as soon as it is discharged from the Graafian follicle. 



The question of the duration of vitality of the spermatozoids, after 

 their passage into the uterus, has an important bearing on the time when 

 conception is most likely to follow sexual intercourse. The alkaline 

 mucus of the internal organs actually favors their movements; the 

 movements are not arrested by contact with menstrual blood ; and, in- 

 deed, when the spermatozoids are mixed with the uterine mucus, they 

 simply change their medium, and there is no reason to believe that they 

 may not retain their vitality as well in the uterus as in the mucus of the 

 vesiculae seminales. It seems impossible, therefore, to fix any limit to 

 the vitality of these anatomical elements, under physiological conditions ; 

 and it is not certain that spermatozoids may not remain either in the 

 vagina or in the Fallopian tubes and around the ovary, when intercourse 

 has taken place immediately after a menstrual period, until the ovulation 

 following. Motile spermatozoids have been observed in the Fallopian 

 tubes as long as twenty-five days after coitus (Diihrssen). The duration 

 of life of an ovum has been estimated at about sixteen days (Issmer). 



Maturation of the Ovum. Before the formation of the polar bodies, 

 the unripe, or immature ovum is called the resting cell. At this time, 



