DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGV. 307 



ovisacs. The membrane of one of these, measuring in its long- diameter -^vth of a 

 Paris line-f", bad a thickness of -g-J-jpth of a line J. When somewhat advanced in size, 

 however, the thickness is sometimes relatively as well as absolutely greater. Yet so 

 transparent is this membrane, that even the form of granules contained in its cavity 

 may be tolerably well observed from the exterior (Plate V. figs. 9. 10. 11. 12. 17-^.) ; 

 the degree of transparency varying with the pressure applied : and when great press- 

 ure has been removed, the previous state in this respect returns, and the vesicle re- 

 sumes more or less completely its natural size, which indicates elasticity as well as 

 susceptibility of distention. This membrane has a kind of undulating surface, pre- 

 senting myriads of depressions or cells, to which is referrible the plaited or folded 

 appearance of the contour, produced by pressure. Neither fibres nor grannies being- 

 found in the texture of this membrane, it is probably without organization. 



The peculiar Granules of the Ovisac. 



8. The only objects which in general are visible (12.) in the ovisac when the latter 

 is first formed, are a few granules (Plate V. figs. 8. 9. 11. 12.^.). These granules de- 

 serve a particular description, from their peculiar appearance, from their entering 

 into the formation of several important structures to be described in Part II. of this 

 memoir, and from their being very intimately connected with the evolution of the 

 ovum from its early appearance as the germinal vesicle (14 — 22.), until as a mature 

 ovum it has passed into the Fallopian tube. 



9. These granules are elliptical or ellipsoidal, sometimes nearly round, and gene- 

 rally flattened (Plate VIII. fig. 73. g.). When lying closely together, their form be- 

 comes by pressure polyhedrons (Plate VI. fig. 44. g^.). They are exceedingly trans- 

 parent, yet often punctate, which latter appearance seems sometimes to arise from 

 the presence of very minute oil-like globules. They present, with more or less distinct- 

 ness, a nucleus ; and I have met with two nuclei in a single granule. In the sub- 

 stance of the nucleus, when highly magnified, there is observable a point still darker 

 (Plate VIII. fig. 73.). These peculiar granules sometimes disappear, apparently by 

 liquefaction ; preparatory to which change I have observed them to become more 

 spherical and brightly pellucid, seeming to contain a fluid in their interior (Plate VI. 

 fig. 44. g^.). In size I have found them to vary from about the 400th to the 100th of 

 a Paris line§, but they are often about the 200th of a Paris line || in length. As viewed 

 with reflected light, they appear greyish white in colour. Water dissolves them. 



10. This is a general description of these very peculiar granules. In some orders 

 of the Mammalia I have found them more regularly elliptic or more round than in 

 others ; in birds I have thought them less regular in form ; in certain animals they 

 have a decided tinge of yellow : but in these respects, as well as in their punctate 

 or subgranulous appearance, and in their stages of liquefaction, their condition 



t = 3^T- of an English inch. + = ^tVt of an English inch. 



§ = Tvo-tr to the t-tVt- of an English inch. II = ttW of an English inch. 



2 r2 



