46 TBB CELL DOCTRINE. 



scarcely say was amply confirmed a little later. But 

 Henle also states, in the same connection, tbat certaiTi 

 cases arise in which perfect cells are developed in a 

 cytobla8tema,in a manner which is inexplicable, and 

 that from these cells tissues are finally developed.* 

 Whence the undetermined state of the question at 

 that time may be easily inferred. Nor is mention 

 here made by Henle of the nucleus of the cell as the 

 pri mary seat of the segmen tation. The su rface of the 

 cell is said to be " constricted " or " furrowed," deeper 

 and deeper, until the division takes place. This de- 

 scription is still adhered to by many physiologists of 

 the preserit day, who consider that there is a simple 

 disappearance of the germinal vesicle or nucleus of the 

 ovum after fecundation, rather than a division of it 

 into two, and substitution of these for the original one. 

 While endeavoring to trace out the steps by which the 

 present most generally accepted views with regard to 

 the origin of cells were arrived at, it must not be for- 

 gotten that other dissenting views were also ad- 

 vanced, though tending differently from those incor- 

 porated in the text, where it is desired more particu- 

 larly to trace those culminating in existing doctrines, 

 '^hus did Reichertf early (1840), dissent from Schwann, 

 since he failed to find the nucleus universally present 

 in the yolk, and he was the first to defend the view 



maintained that the spheres of segmentation are cells which are at 

 first destitute of a cell membrane, though they become invested by 

 one at a subsequent period. 



* Henle, op. cit., p. 177. 



f Reichert, Das Entwickelungsleben im Wirbelthierreioh. Ber- 

 lin, 1840, pp. 6, 93. 



