176 THE CELL-THEORY 



that this small sphere was indeed the mammalian ovum. 

 Ilis discovery was confirmed by Sharpey and by Allen 

 Thomson. Von Baer found the germinal vesicle in the eggs 



o o o 



of frogs, snakes, molluscs, and worms, but not in the 

 mammalian ovum ; he considered the whole mammalian 

 ovum to be the equivalent of the germinal vesicle of birds 

 a comparison rightly questioned by Purkinje (1834). In 

 1834 Coste l discovered in the ovum of the rabbit a vesicle 

 which he considered to be the germinal vesicle of Purkinje ; 

 he observed that it disappeared after fertilisation. 

 Independently of Coste, and very little time after him, 

 Wharton Jones 2 found the germinal vesicle in the 

 mammalian ovum. Valentin in i835, 3 Wagner in i836, 4 

 and Krause in 1837;"' added considerably to the existing 

 knowledge of the structure of the ovum. Wagner in his 

 Prodromus called attention to the widespread occurrence, 

 within the germinal vesicle of a darker speck which he 

 called the Keiinflcck or germinal spot, known sometimes 

 as Wagner's spot. He recognised the Kcimflcck in the ova 

 of many classes of animals from mammals to polyps. 

 Frequently more than one Kcimjlcck occurred. 



Schwann had therefore a good deal of exact knowledge 

 to go upon in discussing the significance of the ovum for 

 the cell - theory. There were two possible interpretations. 

 Either the ovum was a cell and the germinal vesicle its 

 nucleus, or else the germinal vesicle was itself a cell within 

 the larger cell of the ovum and the germinal spot was its 

 nucleus. Schwann had some difficult)' in deciding which of 

 these views to adopt, but he finally inclined to the view that 

 the ovum is a cell and the germinal vesicle its nucleus, 

 basing his opinion largely upon observations by Wagner 

 which tended to prove that the germinal vesicle was formed 



1 Rccherclies sur !<i generation lies Mamniifires. Report by Academy 

 Committee. Ann. >V/. nat. (2) (Zool.~) ii., pp. i-lS, 1834 ; also Einbryo- 

 X<'nic I'l'iiifiart'e, 1837. 



- I.oinL and J'lilin. Phil. M<i. (3) vii., 1835 ; Phil. Trans. 1837. 



:i Handbuch der Entwickelungsgeschichte t 1835, and M tiller's Archiv, 

 1836. 



' rroiiroinns histoHa generati&nis hominis ntijuc aniinaliuin, Lipsiae, 

 1836. 



' Mullcr's Archil', 1837. 



