64 



OBSTE TRIG A L PH YSIOL OGV. 



CHAPTER IV. 



Changes in the Ovum 



During the progress of the ovum towards the uterus, and soon after its 

 reception into that cavity, some remarkable alterations occur. The ovum 

 has encountered the fructifying element of the male semen — the sperma- 

 tozoa ; at least, this has been established in the Rabbit, in whose oviducal 

 ovum they were found to have passed through the zona pelhuida, though 

 no opening has yet been discovered in that extremely fine evanescent 

 film. The germinal vesical disappears, or has changed its character, and 

 a somewhat more opaque embryonal cell succeeds, which may be, or in- 

 cludes, a combination of the nuclear matter of the sperm-cell with that of 

 the germ-cell. Then the vitellus, escaped from its enveloping membrane, 

 becomes depressed in a circular manner, and breaks up into independent 

 masses. 



This change, and others to be described, takes place during the course of 

 the impregnated ovum through the Fallopian tube. It may chance, how- 



Fig. 28. 



Ovum from Oviduct of Rabbit, 

 penetrated by spermatozoa in 

 ITS Vitelline Layer. 



Fig. 29. 



An Ovum more advanced 

 Oviduct. 



ever, that impregnation takes place in the uterus ; for it is probable that 

 the ovum may be retained there for a certain time previous to perishing 

 or being ejected, and that, should it meet the spermatic fluid, impregna- 

 tion will ensue and the usual results follow.* But it is more likely that 

 the initial changes are, in the majority of instances, accomplished in the 

 tube. There, the ovum is bathed and moved about in the clear fluid 

 containing the spermatozoa, by the peristaltic action of the walls of the 

 duct, in order to enable the largest number of the fertilizing particles to 

 obtain access to the yolk, and thus ensure fecundity. 



With the formation of the embryo-cell, the vitellus becomes separated 



* It may be remarked that, with multiparous animals, the number of young in the cornua are not in 

 proportion to the corpora lutea of the same period. Franck mentions an instance in which there were 

 eleven corpora lutea and only five foetuses ; from which it might be inferred that six ova had perished, or, 

 if they had been impregnated, that the foetuses must have died at a very early period, and been absorbed. 

 It has also been stated tj-.at an ovum from the right ovary (which bore recent traces of the rupture of a 

 Graafian vesicle), has been found in the left cornu, whither it must have wandered. This has been 

 observed in woman, in the Bitch, the Guinea-pig, and also in the Sheep. Kehrer mentions, in the 

 Monatsschrift fiir Geburtskunde (vol. xxii., p. 225), finding a fcetus in each horn of the uterus, and in 

 the right ovary two true corpora lutea. One ovum had migrated to the left cornu by means, probably, of 

 the uterine contractions. 



