CHANGES IN THE FECUNDATED OVUM. 799 



Reference 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 inter- 

 nal 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- de- 

 formity 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 recalls 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. 



After fecundation of the ovum, 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. 



Segmentation of the Vitellus. Soon after the fecundation of the ovum 

 and the formation of the vitelline nucleus, a furrow appears at the point of 

 extrusion of the polar globules. This is met by a furrow upon the opposite 

 side, and the vitellus is divided into two globes. One of the globes is 

 slightly larger than the other, and presents fewer and smaller granules. 

 The larger sphere subsequently forms, by its division, the epiblastic cells, 

 and the smaller sphere forms the hypoblastic cells. Each sphere is pro- 

 vided with a distinct nucleus. The two spheres resulting from the first 

 segmentation of the vitellus are divided, each one into two, making four 

 spheres. These spheres are again divided into eight four epiblastic and 

 four hypoblastic spheres each with a nucleus (Van Beneden). One of the 



