896 GENERATION. 



remarkable cases recorded in works upon physiology as instances of deformity due to the 

 influence of the maternal mind are not reliable. It is often the case that, when a child 

 is born with a deformity, the mother imagines she can explain it by some impression 

 received during pregnancy, which she only recalls after she knows that the child is 

 deformed. Still, there are cases which cannot be doubted, but which, in the present 

 state of our knowledge of development and the connection between the mother and the 

 foetus, we cannot attempt to explain. 



Union of the Male with the Female Element 'of Generation. The first important step 

 in our positive knowledge of the mechanism of fecundation was the discovery of the 

 spermatozoids, in 1677, to which we have already referred ; the second was the demon- 

 stration, by Spallanzani, in his experiments upon artificial fecundation, that, when the 

 seminal fluid is carefully filtered, the liquid which passes through has no fecundating 

 properties, the male element remaining on the filter ; and the third was the demonstra- 

 tion of the presence of spermatozoids within the vitelline membrane, showing that fecun- 

 dation consists in a direct union of the male with the female element. 



As to the mechanism of the penetration of spermatozoids to the vitellus, we can only 

 refer to the micropyle discovered in the ova of fishes and rnollusks, which we have 

 already described. In the ova of the Nephelis, a small species of leech, Robin has seen 

 spermatozoids, to the number of several hundreds, penetrate the vitelline membrane, 

 always at one point, continuing their movements upon the surface of the vitellus. 

 " Almost always, when the penetration has ceased, a bundle of spermatozoids are 

 arrested in the micropyle." We had an opportunity of witnessing a demonstration of 



these phenomena by Prof. Robin, in 1861, in the ova 

 of the Limnteus stagnalis, and actually saw a sper- 

 matozoid half-way through the vitelline membrane. 

 According to numerous direct observations, the sper- 

 matozoids move actively around the ovum, collect 

 toward a certain point, and there penetrate the vitel- 

 line membrane. Coste, and many other observers 

 whom it is unnecessary to quote, have seen the sper- 

 matozoids within the vitelline membrane, in the ovum 

 of the rabbit ; and, more recently, Weil has seen sper- 

 matozoids wedged in the substance of the zona pellu- 

 cida, has added blood to the specimen under observa 

 tion, and has restored the movements of the sperma- 

 FIG. 287. Penetration of spermatozoids tozoids while in this position. He has also seen, in 



through the vitelline membrane. n ,-\ j . j ,-\ 



(Haeckoi.) some instances, perfectly-formed spermatozoids m the 



very substance of the vitellus. 



All direct observations upon the lower orders of animals have shown that several sper- 

 matozoids are necessary for the fecundation of a single ovum; but we have no definite 

 idea of the number required in mammals, much less in the human subject. Nor do we 

 know what becomes of the spermatozoids after they have come in contact with the vitel- 

 lus. All that we can say upon this point is, that there is probably a molecular union 

 between the two generative elements, soon to be followed by the remarkable series of 

 changes involved in the first processes of development. 



Segmentation of the Vitellus. 



As we have already stated, it is probable that tlje 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 sper- 

 matozoids do not penetrate the vitelline membrane near the ovary, it presents an obstacle 



