THE DEVELOPMENT OF THE EMBRYO 1137 



The fact that the spermatozoa are capable of making their own way- 

 through the canal of the cervix into the uterus is proved by the cases 

 of pregnancy following incomplete coitus, and especially by the preg- 

 nancies which have occurred in women possessing perfect hymens. 

 Nevertheless, it has been thought by Litzmann, and others, that the 

 uterus contracts and relaxes at the height of the orgasm and actually 

 aspirates the semen into its cavity. Moreover, Kristeller^ has advo- 

 cated the view that a mucus plug is projected at this time from the 

 mouth of the cervix, which is then retracted, carrying with it large 

 numbers of spermatozoa. 



The Place of Meeting of the Ovum and Spermatozoa. — The view 

 that the fertilization of the ovum is effected within the cavity of the 

 uterus, has now given way to the belief that the meeting between the 

 male and female sperm-cells takes place in the Fallopian tube and 

 chiefly in its funnel-shaped outer extremity. Since the distance 

 between this point of the generative tract and the mouth of the uterus 

 measures only about 16 cm., the spermatozoa may reach this receptacle 

 in less than 1 hour. In fact, the occurrence of ovarian pregnancy 

 in woman demonstrates that these elements may even advance as 

 far as this organ and that the fimbriated extremity of the tube is not 

 absolutely impermeable. This view, that impregnation takes place in 

 the Fallopian tube, also finds substantiation in the fact that living 

 spermatozoa have frequently been found here; in fact, they have been 

 noted to live within its lumen for an almost indefinite period of time. 

 In the tubes of the bat, for example, they have been known to retain 

 their activity for many months. 



The Implantation of the Ovum. — After its fertilization the ovum 

 undergoes repeated segmentation and slowly progresses into the uterus 

 where it remains until the end of the period of gestation. It tra- 

 verses this distance in about 8 days after its impregnation, having 

 meanwhile attained a diameter of 0.2 mm. and completed the morula 

 stage. 2 The earliest specimen of developing ova has been described 

 by Bryce and Teacher. ^ It measured 0.77 mm. in length and 0.63 

 mm. in breadth, and was about 13 days old. This one, as well as all 

 the others representing a later stage of development, were found 

 deeply imbedded in the decidua and hence, well removed from the 

 cavity of the uterus. Spee, ^ therefore, assumes that the human ovum 

 attaches itself to the free surface of the endometrium and destroys 

 the underlying tissue by means of a tryptic ferment.^ In this way it 

 gradually sinks into the depth of the uterine decidua, its point of 



1 Berliner klin. Wochenschr., 1871. 



2 Grosser, Vergl. Anat. und Entwickelungsgesch. der Eihaute und Placenta, 

 Leipzig, 1909. 



3 Early development and imbedding of the human ovum, Glasgow, 1908; 

 also Linzenmeier, Archiv fiir Gynec, cii, 1914, 1 



^ Zeitschr. fiir Morph. und Anthropol., 1901, and Verh. deutsch. Ges. fiir 

 Gynec, 1906. 



^ Grafenberg, Zeitschr. fiir Geburtshilfe und Gynec, 1910. 



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