[88] 



OVUM. 



Fig. 61 . 



the cow. Upon the question how far these 

 varieties in the structure of the ovum may be 

 supposed to be related to the origin of Double- 

 monsters and Twins, I must refer to Pro- 

 fessor Vrolik's interesting article Teratology.* 

 For the assistance of those who may wish 

 to engage in researches of the same nature as 

 those by which the above facts have been as- 

 certained, I will state shortly the manner in 

 which the ova of Mammalia may be procured 

 either from the ovary or after they have left 

 that organ. 1st. For the examination of the 

 earlier ovarian ova and follicles, thin sec- 

 tions of the ovarian substance are to be 

 made, especially towards the surface of the 

 ovary; and some of these are to be teased 

 out with needle points, and examined with 

 the aid of compression, &c. 2nd. For the 

 more mature ovarian ovum, &c., the outer 

 covering of the ovary is to be removed 

 from the surface of one or more of the pro- 

 minent follicles ; and the latter may then, if 

 large, be carefully dissected out of the ovary, 

 and laid on a glass plate, where it is to be 

 opened with a sharp-pointed knife, and its 

 contents are to be gently pressed out on 

 the glass. The ovum may in general be 

 easily detected in a part of the tunica granu- 

 losa with a low magnifying lens, or even 

 sometimes with the naked eye. In the ovary 



vitellus jfo" ; the germinal vesicle fa" ; the ma- of the dog the ovum may sometimes be seen 

 cula yjLj" ; thickness of the zona yfaf. The ovum without any dissection towards the most 



Ovarian ovum of the Sow. 



This ovum is represented in order to show the 

 peculiar pyriform shape of the macula iu the ger- 

 minal ves'icle, to the wall of which the macula 

 appears to be attached. This ovum was taken 

 from a Graafian follicle of T L" in diameter. The 

 following are the dimensions of its several parts 

 which are magnified 250 diameters in the figure. 

 The ovum across the exterior of the zona " ; the 



is surrounded by the thick layer of cells which 

 form the granular disc, dp. A few cells of the 

 thinner membrana granulosa are represented at tg. 



to occur in the germinal vesicle during the 

 ovarian existence of the ovum. It usually 



prominent part of the surface of the ma- 

 ture follicles, t 3rd. To procure the ova 

 after they have left the ovary, or while they 

 are in the tubes, two methods may be pur- 

 sued : either the whole length of the tube 



disappears in Mammalia previous to the es- *f be .P ened * ith very finely-pointed and 



cape of the ovum from the Graafian follicle ; shar P SCIS ? ors > and r th surface * hen s P read ? ut 



and examined carefully with a low magnifying 



power under a good elumination, but this 

 must not be done under water ; or another 



but in this class of animals the phenomena 

 attending the disappearance have not yet 

 been fully investigated. There are some 

 ids fc 



grounds for believing that immediately pre- P 

 vious to the bursting of the vesicle there may 

 be changes of the macula and other contents 

 of the vesicle of a corresponding nature with 

 those which have been more clearly observed 

 in Batrachia and Fishes. Dr. Martin Barry 

 seems to have observed something of this 

 kind, and M. Coste has figured, but not so far 



r be followed according to the re- 

 commendation of Martin Barry, founded on a 

 suggestion thrown out by Cruickshank, as 

 follows : The Fallopian tubes being divided 

 into several portions, the contents of each 

 portion are to be separately pressed out by 

 passing a blunt instrument firmly along the 

 outside of the tube, and, being placed on suit- 



as I am aware described, the development of able P lates of glass, are to be subjected to the 

 cells in the germinal vesicle of a ripe ovarian necessary examination. The latter method 



human ovum. 



R. Wagner states, that occasionally a double 

 macula may be seen in the germinal vesicle. f 

 I have on one occasion observed two germinal 

 vesicles within the same ovum in the dog. 



Bischoff has on three occasions observed 

 two ovules in the same Graafian follicle of the 

 rabbit. "| This had been previously noticed b 

 Von Baer in the dog and pig. And Bidder 

 detected two ovules embedded in the same 

 granular membrane of one Graafian vesicle of 



* See the'plate in his great work marked " Mam- 

 miferes ; Homme." PI. J. Fig. 6. 



is particularly convenient in small animals : 

 in the larger I have followed both plans. 

 The method of Barry certainly saves much 

 time and trouble, and is on the whole sure 

 enough.]; 4th. Of the plan for obtaining the 

 ova from the uterus, when of considerable size, 

 as it belongs rather to the history of develop- 

 ment, I will only say here that the greatest 

 caution is necessary in cutting through the 

 walls of the uterus in different layers so as to 



p. 973. Cyclopaed. of Anat. and 



* Vol. 

 Physiol. 



t See Von Baer's Commentary on his Epistola, 



f See Prodromus Hist. Generationis, Fig. xxxi. in Breschet's Repertoire, 1828, p. 38. 

 j Muller's Archiv. Jahrsbericht, p. 1G9. J See Barry's Second Series of Researches, &c., 



Mttller's Archiv. 1842, p. 86. 



Phil. Trans. 1839, p. 366. 



