262 THE CELL-THEORY 



233, 236), and that they may be exhibited by different portions of these 

 soHd constituents, and to a different extent by these different portions 

 (p. 233) ; proving hereby, very clearly, as it seems to us, that the forces 

 in question are not centralized in the cells, but are resident in their 

 component molecules. All Schwann's able comparison of cell-develop- 

 ment with crystallization tends, in fact, to the same conclusion. When 

 matter crystallizes from a solution, the presence of a foreign body may 

 determine the place and form of the deposit ; but the crystals themselves 

 are the result, not of the attractive forces of the foreign body, but of 

 the forces resident in their component molecules. So in cell-develop- 

 ment, if it is to be rigorously compared to crystallization, even if the 

 nuclei represent the foreign bodies, which determine the place of the 

 chemical and morphological alterations in the surrounding substance, 

 it by no means follows that they are their cause. 



Kolliker(§§ 11, 13), resting especially upon the phenomena of yelk- 

 division and of endogenous cell-development, advocates the existence 

 of a peculiar molecular attraction proceeding from the nucleolus first, 

 and subsequently from the nucleus. Now as regards endogenous 

 cell-development, we must confess that we can find no more ground 

 for its occurrence among animals than among plants. Xageli's cell- 

 development around portions of contents, upon which Kolliker lays 

 so much stress, is nothing more than a case of division of the endoplast 

 (primordial utricle) and subsequent development of periplastic substance 

 round the portions. In cartilage, which is so often quoted as offering 

 marked endogenous cell-development, we must agree with Leidy and 

 Remak, that nothing but division of the endoplasts (nuclei, primordial 

 utricles) and ingrowth of the periplast (intercellular substance, cell- 

 wall) occurs. In these endoplasts again, the very existence of a nucleus 

 is in the highest degree variable and inconstant, and division occurs 

 as well without it as with it. 



The process of yelk-division — that remarkable manifestation of a 

 tendency to break up, in the yelk of most animals, into successively 

 smaller spheroids, in each of which a nucleus of some kind appears — 

 seems, at first, to offer very strong evidence in favour of the exertion 

 of some attraction by these nuclei upon the vitelline mass. But we 

 think that a closer examination completely deprives this evidence of all 

 weight. In the first place, the appearance of the nuclei is in many 

 cases subsequent to segmentation. It is thus in Strongylus auricularis 

 (Reichert), in Phallusia (Krohn), in the hen's egg (Remak). In the 

 second place, it seems difficult to conceive any mode of operation of a 

 central attractive force which shall give rise to the phenomena of 

 segmentation, for the resulting spheroids always pass into one another 



