CELLS. 21 



nucleus; or, in the second place, the latter may become sur- 

 rounded by a greater or smaller quantity of solidifying cyto- 

 blastema, and it is only round this enveloping mass, which I 

 have called an investing globule, that a membrane forms. This 

 last occurrence in the free cell-formation has hitherto been 

 observed only in the ovum, in which the germinal vesicle, 

 i. e. the nucleus of the egg-cell, being first formed, surrounds 

 itself with some yelk before the vitellary membrane appears. 

 On the other hand, cell-development directly round the nucleus 

 takes place in all the other localities which have been men- 

 tioned above, and is demonstrated by the occurrence, among 

 free nuclei and large cells, of very small cells, which closely 

 invest the nucleus or are but little separated from it. It may, 

 however, be remarked, that perhaps in these cases also, the 

 cell-membranes at their origin are separated from the nuclei 

 by a very small quantity of cytoblastema, so small as to be 

 incapable of detection. 



[Free cell-formation is exceedingly frequent in pathological 

 productions, and the cells in pus and in exudations of all kinds 

 arise in this manner; in fact, all pathological cell-formation 

 properly comes under this head. Usually the cell-membranes 

 here arise directly round the nucleus, less commonly as it 

 would seem round investing globules. With regard to phy- 

 siological processes, as has been already shown, free cell-deve- 

 lopment has been much too readily taken for granted ; and 

 especially as regards the epithelial and horny tissues, as 

 well as in many glandular secretions, it has been assumed 

 without any sufficient grounds. Botany knows no free cell- 

 development.] 1 



1 [There cannot be said to be any evidence of the occurrence of free cell-development 

 in animals, so long as in any case cited it is not shown that the first-formed particles 

 which make their appearance cannot have derived their origin from pre-existing 

 formed particles, either by the detachment or fission of the latter. Not only does 

 this condition remain unfulfilled for all the instances cited, but it has not been 

 attempted, and would seem to be impossible. In pathological exudations, for instance, 

 who shall determine that the first structural elements which appear, granules, free 

 " nuclei," exudation corpuscles, &c, are not directly derived either from the blood, or 

 from the tissue into which the exudation has taken place ?— Eds.] 



