History of the development of the human ovum, with a comparative view of the development of the ova of mammalia and birds / translated and abridged from the German of G. Valentin ... by Martin Barry.

  • Valentin, G. (Gabriel), 1810-1883.
Date:
[1834?]
Catalogue details

Licence: Public Domain Mark

Credit: History of the development of the human ovum, with a comparative view of the development of the ova of mammalia and birds / translated and abridged from the German of G. Valentin ... by Martin Barry. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    3. The foundation of the Germinal membrane.—In the ovum of the fowl which is so far advanced in its development that it is leaving the ovary and entering the oviduct, there is seen through the membrane of the yolk a grayish white circular spot, which from early times has been known under the name of the macula or cicatricula. If the ovum be lacerated, and its content mi- nutely examined, the cicatricula is found like a grayish white disk, which in its whole periphery is dense, granulous and opaque, but in the centre presents a clear non-granulous, and perfectly diaphanous point. This observation was made so long since as by Fabricius ab Aquapendente, Harvey, and others, and has been repeated with ease by very many other naturalists. Purkinje, who, in 1825, again entered upon researches on the unincubated egg of the bird, was so fortunate as to place the relation of this transparent, non-granulous point in a clearer light. He found, namely, that when he removed the dark granulous mass, by suction with a small tube, there remained a perfectly transparent vesicle, filled with a pelkicid lymph, which had a decidedly spherical form, but being extremely delicate, was very easily la- cerated, and its fluid escaped. As he found this, which later natm-alists have named, after its discoverer, the Purkinjean vesicle, in the ova of the ovary, but could not see it in ova which had already entered the oviduct, he assigned to it the name of germinal vesicle. This germinal vesicle is imbedded in the granulous layer of the cicatricula, so that the latter forms a de- pression around it, but which depression, viewed from above, appears like a circle, surrounding the vesicle. With that portion of its surface directed outwards, the germinal vesicle touches the internal surface of the yolk-bag, without being or- ganically connected with it. The disk which surrounds it con- sists of many minute granules, lying closely together, and unit- ed by a transparent, tenacious matter, appearing at first sight circumscribed in the form of a round or oval disk. Rut when this disk is examined with aplanatic lenses, while within the un- injured ovum, it appears probable that the granulous layer ly- ing on the internal surface of the yolk-bag is a continuation of the disk, the granulous layer, situated between the yolk-bag and the yolk itself, every where embracing and enclosing the latter. The granulous membrane,—its thickened portion, the so-called cicatricula,—and the germinal vesicle, constitute those parts of the ovum which pass immediately into the original foundation of the embryo, the blastoderma or germinal membrane. We shall therefore assign to the tout ensemble of the parts now mentioned, the name of Germinal membrane (Keimanlage,) dis- tinguishing in it, Istly, The granulous layer under the yolk-bag.