DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
559 
the production of the germ. With regard to the former, I remain in a state of 
entire uncertainty, and can only say that I observed that vesicle in mature ova [of 
the Crafish] as late as in November, but have found no trace of it in the following 
March. The disappearance of the vesicle therefore takes place some time before the 
ovum leaves the ovary. With regard to the germ, it appears first to originate when 
the germinal vesicle disappears, and perhaps — as Von Baer with reference to animals 
in general has conjectured — since that vesicle bursts, its walls are dissolved, and its 
contents supply the foundation of the germ-f-”. “Of the Purkinjean vesicle in the 
laid ova of Oniscus aquaticus, I have not been able to detect the least trace];.” “ I 
remain in entire doubt whether the ovum [of Oniscus asellus~\ brings with it into the 
brooding cavity a germ. But when the ovum has reached that cavity a Purkinjean 
vesicle is no longer to be found 
414. Carus states that the germinal vesicle “ on the separation of the ovum from 
the ovary*** becomes destroyed, and forms the fluid ( Colliquamentum Malpighii) 
under the germinal membrane, which then yields the essential substance for the for- 
mation of the embryo ||.” 
415. Burdach. “ But the ovum itself undergoes in its essential parts a change, 
through which the immediate foundation of the new being, namely, the germinal 
membrane, is formed : that is, the germinal vesicle, which has passed nearer and 
nearer to the circumference of the ovum and applied itself to the germinal layer, 
finally disappears, no doubt bursting and pouring its fluid into the germinal layer, 
whereupon the germinal membrane forms. Thus Purkinje found in the ovum of the 
Bird, when the infundibulum of the oviduct had received it, that the germinal vesicle 
had disappeared, and the germinal elevation (Keimhugel) with its opening become, for 
the most part, effaced ; but that in the passage of the ovum through the oviduct, the 
germinal elevation became fully dissolved, its accumulated granules gave way, and in 
their stead there appeared the uniform, dense, semi-transparent germinal membrane, 
Further observations have shown that in all other animals also, the germinal vesicle 
vanishes before the appearance of the germinal membrane ; and we may, therefore, 
with Purkinje and Von Baer, regard it as the bearer of the female generative power. 
But by what means its bursting is determined is still unexplained^.” 
416. Valentin demonstrated the existence — first announced by Coste — of a vesicle 
in the mammiferous ovum, corresponding to that of Purkinje in the Bird. “ The 
germinal vesicle [in the ovum of the Bird]” says Valentin, “becomes invisible. It 
probably bursts, and pours its fluid first of all into the disc. It is not, therefore, 
f Ueber die Bildung und Entwickelung des Flusskrebses, p. 2, 1829. 
| Abhandlungen zur Bildungs-und Entwickelungsgeschichte des Menschen und der Thiere. Erster Theil, 
p. 4, 1832. 
§ Abhandlungen, &c., Zweiter Theil, p. 72, 1833. 
|| Erlauterungstafeln zur vergleichenden Anatomie. Heft III., p. 21, 1831. 
Die Physiologie als Erfahrungswissenschaft, Erster Band, S. 550. 551, 1835. 
