CHANGES IN THE FECUNDATED OVUM. 799 



Eeference has already been made to the curious fact that when a cow 

 produces twins, one male and the other female, the female, which is called a 

 free-martin, is sterile and presents an imperfect development of the internal 

 organs of generation. This has led to the idea that possibly the same law 

 may apply to the human subject, in cases of twins, one male and the other 

 female ; but many observations are recorded in gynaecological works, showing 

 the incorrectness of this view. 



It has long been a question whether impressions made upon the nervous 

 system of the mother can exert an influence upon the foetus in utero. While 

 many authors admit that violent emotions experienced by the mother may 

 affect the nutrition and the general development of the foetus, some writers 

 of authority deny that the imagination can have any influence in producing 

 deformities. The remarkable cases recorded as instances of deformity due to 

 the influence of the maternal mind are not entirely reliable ; and it often 

 happens that when a child is born with a deformity, the mother imagines she 

 can explain it by some impression received during pregnancy, which she re- 

 calls only after she knows that the child is deformed. There is, indeed, no 

 satisfactory evidence that the maternal mind has anything to do with the 

 production of deformities in utero. 



CHANGES IN" THE FECUNDATED OVUM. 



It is probable that the ovum is fecundated either just as it enters the 

 Fallopian tube or in the dilated portion, near the ovary. 'As it passes down 

 the tube, whether it be or be not fecundated, it becomes covered with an 

 albuminous layer. This layer probably serves to protect the fecundated 

 ovum, and when the spermatozoids do not penetrate the vitelline membrane 

 near the ovary, it presents an obstacle to their passage. Shortly after fecun- 

 dation the germinal vesicle disappears ; but this occurs in ova that have not 

 been fecundated. Soon after ovulation, also, the vitellus gradually withdraws 

 itself from certain portions of the vitelline membrane, or becomes deformed, 

 and then often rotates upon itself. The deformation and gyration of the 

 vitellus, however, have been observed in ova before fecundation. They are 

 of the class of movements called amoeboid. 



After the penetration of spermatozoids and their union with the vitellus, 

 at least in many of the lowest forms of animals, the appearance of the vitellus 

 undergoes a remarkable change, by which ova that are about to pass through 

 the first processes of development may readily be distinguished from those 

 which have not been fecundated. This change consists in an enlargement 

 of the granules and their more complete separation from the clear substance 

 of the vitellus. The granules then refract light more strongly than before, 

 so that the fecundated ova are distinctly brighter than the others. This is 

 the first appearance that is distinctive of fecundation. 



Polar Globule. The next process observed in the ovum is the separation 

 from the vitellus, of a comparatively clear, rounded mass, called by Kobin the 

 polar globule. This body has been observed by various anatomists and de- 

 scribed under different names. The exact mode of its formation has been 



