40 THE CELL DOCTRINE. 



2. By endogenous cell development (durch endo- 

 gene Zeugung), where the cell contents of the mo- 

 ther cell become the cytoblasterna 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- 

 graph* immediately following, "We would, with 

 Schwann, consider cell formation in the yolk, by 

 6 farrowing,' an analogous process, if we may con- 

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

 to describe how, by a "cording in"f of the surface, 

 the yolk is divided into two equal parts, these into 

 four, and so on until the entire yolk becomes a mul- 

 berry mass, made up of little round bodies. This seg- 

 mentation of the ovum already observed in the yolks 

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

 this time (1841), has perhaps merely escaped noticej 

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

 pected by Bergman, a suspicion which we need 

 scarcely say was amply confirmed a little later. But 

 Henle also states, in the same connection, that certain 

 cases arise in which perfect cells are developed in a 

 cytoblastema, in a manner which is inexplicable, 

 and that from these cells, tissues are finally devel- 

 oped. Whence the undetermined state of the question 



* Henlo, op. cit., p. 176. 



f Einschniiren, to cord (a box, &c.), to bind with a cord, to 

 string. Orieb. 



J Henle, op. cit., p. 177. 

 % Henle, op. cit., p. 177. 



