34 THE UNIMPREGNATED OVUM. 



structureless membrane, or a layer of albuminous fluid enclosed between 

 two thin membranes, seems now to be resolved. Wagner, * Bischoff,t 

 Henle, J Barry, and Wharton Jones, || all adopt the former view respect- 

 ing the nature of this part. 



It is still, however, a disputed question whether internal to the zona 

 pellucida there is not a second membrane enclosing the mass of yolk. 

 Dr. Herman Meyer has stated ^[ that after he had completely dissolved the 

 zona pellucida of an ovum, by the agency of a solution of potash, he rup- 

 tured the yolk, and allowed the yolk-granules to escape, and then saw 

 a thin granulated membrane remaining, which had formed the proper 

 investment of the yolk. Bischoff, however, has repeated this experiment, 

 and affirms that in ova of the sow, cow, bitch, and rabbit, solution of potash 

 does not dissolve the zona pellucida, but only produces contraction and con- 

 densation of it.** Meyer's observation seems, therefore, to have been an 

 erroneous one; and as the membranes of which Dr. Barry has described ff 

 the successive formation and disappearance on the interior of the zona 

 pellucida, cannot be regarded as constituting an essential part of the ovum, 

 all proof of the existence of any membrane internal to the zona pellu- 

 cida, derived from actual observation, fails. Wagner JJ infers that such 

 membrane exists, from the fact that an interval can sometimes be seen be- 

 tween the zona pellucida and the yolk, and that the latter has then 

 a very defined outline. But Bischoff, as we shall presently see, gives a 

 different explanation of this appearance, and denies positively that there is 

 any other membrana vitelli than the so-called zona pellucida. Wharton 

 Jones,|||| Coste, and Henle entertain the same opinion. 



The yolk is described by Henle 1FH" as being composed of granules and 

 globules of different sizes, imbedded in a more or less fluid substance. The 

 smaller granules, which are the more numerous, in their appearance as well 

 as their constant motion, resemble pigment granules. The larger granules 

 or globules, which have the aspect of fat globules, are in greatest number 

 at the periphery of the yolk. The number of the granules is, according to 

 BischofTs observations, greatest in carnivorous animals. In the human 

 ovum their quantity is comparatively small. 



The substance that combines the globules and granules of the yolk is, in 

 many animals, quite fluid. The yolk then completely fills the cavity of the 

 zona pellucida, and escapes in a liquid form when that membrane is rup- 



* Lehrbuch der Physiologic, 2 te Ausgabe. Leipzig, 1843, p. 37. 



t Entwickelungs-geschichte, p. 12; and more recently in his Entwickelungs-gesch. des 

 Hunde-eies, 1845, p. 9. J Allgemeine Anatomie, p. 965. 



Researches on Embryology. || Lond. and Edinb. Phil. Mag. 1835, p. 209. 



t Muller's Archiv. 1842, p. 18. ** Op. cit. p. 553. 



tt The views of Dr. Barry are explained in the notes at pages 1499 and 1514 of Muller's 

 Physiology. Jt Op. cit. p. 37. $$ Op. cit. p. 14. 



Illl Med. Gazette, vol. xxi. and vol. xxiv. 1 U Allgemeine Anatomie, p. 966. 



