THE CELL DOCTRINE. 45 



had hesitatingly, if at all, accepted it as a rare 

 method of cell formation. 



Henle,* who, in general, adopted the view of 

 Schwann as to the ■primary origin of cells, though he 

 made exception to its universality of application, 

 says that ceils multiply in three ways: 



1. By budding (durch Sprossen), as in certain lower 

 plants. 



2. By endogenous cell development (durch endo- 

 gene Zeugung), where the cell contents of the mother 

 cell become the cytoblastema of the daughter cells, 

 as originally given by Schleiden and Schwann. 



3. By division or segmentation (durch "Theilung), 

 of which he says, however, no examples are found 

 among animals ; though he also states in the para- 

 graphf immediately following, " We would, with 

 Schwann, consider cell formation in the yolk, by 

 ' furrowing,' an analogous process, if we may con- 

 sider the yolk as a simple cell." He then proceeds 

 to describe how, by a constriction of the surface, the 

 yolk is divided into two equal parts, these into four, 

 and so on until the entire yolk becomes a mulberry 

 mass, made up of little round bodies. This segmen- 

 tation of the ovum already observed in the yolks of 

 frogs, fish, molluscs, and medusse, Henle says at 

 this time (1841), has perhaps merely escaped notice:}: 

 in the case of the higher animals, as plausibly sus- 

 pected by Bergmanu,§ a suspicion which we need 



* Henle, Allgemeine Anatomie. Leipzig, 1841, p. 172 et seq. 

 •j- Henle, op. cit., p. 176. J Henle, op. cit., p. 177. 



J Bergmann, Miiller's Arehiv, 1841. Bergmann also in this 

 paper objected to the existence of a cell membrane, and correctly 



