DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGY. 325 



81. Every observer who has burst a Graafian vesicle under the microscope must 

 have noticed the mass of granules that always escapes with the ovum. Von Baer, 

 indeed, mentions "shreds" formed of g-ranules as being visible in the mass thus 

 escaping. The structures I have just mentioned (retlnacula) (Plate VII. fig. 50. g-.) 

 explain the nature of the escaping mass of granules, and the "shreds" observed by 

 Baer, which latter appear to have been the ruptured retinacula. 



82. When describing the membrana granulosa (74.), I stated it to be sometimes of 

 very unequal thickness, and to present villi projecting from its inner surface into the 

 fluid of the Graafian vesicle. If Plate VII. fig. 50. ^^ and g^ be again referred to, 

 and the manner of origin, as I suppose, of the membrana granulosa borne in mind, 

 the cause of those inequalities in the thickness of the latter will be evident. The villi 

 on the internal surface of this membrane are nothing more than the remains of the 

 retinacula, broken off" as these are when the contents of a Graafian vesicle escape-|~. 



83. The retinacula as now described, extending from the membrana granulosa to 

 the centre of the Graafian vesicle, are in most animals very indistinctly seen, and 

 hence it is that they have been hitherto overlooked. I first saw them in the Rabbit, 

 and to those who may wish to convince themselves of their existence I recommend 

 this animal, from the comparative distinctness with which they are here seen (Plate VII. 

 fig. 50. g^.). They are very distinct also in the Ferret (Mustela Euro) ; less so, yet 

 visible, from the exterior of the ovisac in the Ruminantia (figs. 51 and 52. g-.) : and 

 having never failed to find some trace of them, it is my opinion that these structures 

 are general in the class Mammalia J. 



84. Very often when the central mass is visible, and the ovum distinct within it, 

 nothing is seen of the cord-like portions of the retinacula. This is sometimes owing 

 to the size of the Graafian vesicle rendering the object too remote, or to the imperfect 

 transparency of its membranes, and sometimes to undue pressure having been ap- 

 plied, which breaks the cord-like portions down. Care must be taken, when they are 

 sought for, to apply no more pressure than is absolutely needful ; and perhaps the 

 general remark may not here be out of place, that even with the most careful mani- 

 pulation these parts may sometimes become displaced. Dissecting out a Graafian 

 vesicle, stripping off" the peritoneal covering of the ovary, or slicing and even handling 

 the latter, tend to disturb the exquisitely suspended ovum. 



The Ovum conveyed to the 'periphery of the Qraafian Vesicle. 



85. From the centre of the Graafian vesicle the ovum passes to its periphery. This 

 change of place is gradual, and the same structures which we have seen to suspend 

 the ovum in the former situation convey it to the latter. In Plate VII. fig. 55. this 



t Although for the sake of perspicuity I have thought it hest to distinguish the membrana granulosa and 

 retinacula by two appellations, I think they are but parts of the same structure. 



X I have seen these structures (as well as the tunica granulosa) in the Goat, the Hedgehog, and the Human 

 subject. 



