[122] 



OVUM. 



Nelson,* a peculiar softening of the ova, which 

 may be caused by the rapid imbibition of fluid 

 at the time the changes above mentioned are 

 taking place, renders them peculiarly liable to 

 be impressed by the spermatic corpuscles at 



Fig. 87*. 



Development of ova in Mernris albt'cans, belonging to 

 the Gordiacei. (From Meissner.} 



a. Germ-cells from the upper or coecal end of the 

 ovarian tube, their nuclei undergoing subdivision. 



b. Various stages of farther multiplication of the 

 internal cells, which in the more advanced are seen 

 to approach the surface of the original cell, and to 

 cause the bulging of its membrane by the enlarge- 

 ment of the internal cells, which last constitute 

 the primitive ova. 



* Loc. cit., p. 576. 



c. d. Groups of primitive ova thus formed ; some 

 of them much more developed than others, present- 

 ing internally the nucleated germinal vesicles and 

 yolk'granules and attached in pediculated capsules, 

 which are formed by the extension of the membrane 

 of the primary germ cells. 



e. A group of these ova more advanced; the 

 opaque granular yolk increased in quantity so as to 

 obscure in part the germinal vesicles ; the pedicles 

 much narrowed and somewhat elongated ; the ex- 

 ternal ova are nearly mature ; those in the centre 

 remain abortive. 



f. Two similar ova now ripe, a part of one of 

 them is artificially burst, showing the escape of the 

 yolk granules and germinal vesicle with a double 

 macula. The remains of the pedicles when detached 

 from the central mass constitute, according to 

 Meissner, the micropyle aperture. 



this period; and Nelson is of opinion that 

 these corpuscles even penetrate completely 

 into the yolk-substance, and ultimately com- 

 bine with it. Little doubt can be entertained 

 that a combination of the spermatic and vitel- 

 line elements in some manner takes place at 

 this time, whether by the direct interpene- 

 tration after the mode described by Nelson, 

 some may be inclined to doubt; but at all 

 events the spermatozoa act immediately on 

 the vitelline substance at this stage of the 

 progress of the ovum. * 



As the ovum descends in the next part of 

 the tube or uterus, the external membrane 

 becomes more dense, additional layers are 

 deposited upon it, and at last it acquires more 



* Professor Bischoff has, in his recently published 

 tract " Wiederlegung des von Dr. Keber bei den 

 Naiaden und Dr. Nelson bei den Ascariden behaupte- 

 ten Eindringens der Spermatozoiden in das Ei," &c., 

 Giessen, 4to., 1854, called in question the accuracy 

 of Nelson's observations, and asserted that Nelson's 

 spermatozoa are only epithelial particles belonging 

 to the female passages. In a subsequently pub- 

 lished paper, entitled, " Bestatigung des von Dr. 

 Newport bei den Batrachiern und Dr. Barry bei 

 den Kaninchen behaupteten Eindringens der Sper- 

 matozoiden in das Ei, Giessen, 25th March, 1854," 

 although Bischoff has seen reason to alter his pre- 

 vious views as to the phenomena of fecundation in 

 the Ascaris mystax, he still in that paper, and in a 

 special memoir on the subject, published in the 

 Zeitsch. fur Wissensch. Zool., 1854, vol. vi. p. 377. 

 adheres to the view that the bodies which I, along 

 with Nelson and Meissner, regard as spermatozoa 

 are no more than epithelial cells. I have elsewhere 

 shown that this view is altogether untenable, and 

 that no doubt can now prevail as to the corpuscles in 

 question being the product of development from 

 the spermatic cells of the male Ascaris, and as to 

 the possibility of their direct action on the ova 

 within the female previous to the formation of the 

 vitelline membrane. Meissner has also given 

 the most satisfactory evidence on the same point 

 in his memoir on the penetration of the sperma- 

 tozoa into the ova of animals, contained in the 

 same volume of the last quoted work, though this 

 author takes a different view from Nelson and my- 

 self as to the manner in which the spermatozoa are 

 admitted into the ovum in Ascaris mystax, believing 

 in the existence of a vitelline membrane and micro- 

 pyle, in the same manner as in Mermis and other 

 Gordiacei, which he has so well described. With 

 regard to this view as applied to the Ascaris mystax, 

 Bischoff's observations, Nelson's, and my own, give 

 me the greatest confidence in asserting that there is 

 at first no vitelline membrane in this animal at the 

 time when the ova first meet with the spermatic 

 corpuscles. 



