56 GENERAL ANATOMY OF THE TISSUES. 



the structure of simple cells, and the nucleus-like body they contain 

 takes a share in the process of cell division, like that of the cell-nucleus 

 in common cells. In pathological formations cell division has not yet 

 been observed. In the vegetable kingdom it is rare, and has been seen 

 only in the lower organisms ; unless, indeed, we are to reckon here the 

 constriction of the primordial utricle observed by Von Mohl in the course 

 of endogenous cell-development.* 



§ 18. Theory of Q ell-development. — Among the few hypotheses which 

 have, up to the present time, been proposed in explanation of the develop- 

 ment of cells, that of Schwann, who compares it with the formation of crys- 

 tals, is certainly the most attractive. Without overlooking the differences 

 between a crystal and a cell, which chiefly consist in the former being 

 solid and homogeneous, in its growing by apposition, and in its being 

 bounded by plane surfaces and angles, Schwann endeavors to explain 

 cell-development as a crystallization of organic matter, and to deduce 

 from the permeability of the latter the differences in the phenomena 

 presented by the two. In a fluid containing organic matters dissolved 



* [There can, we think, be little doubt that Von Mohl is quite correct in the view he takes 

 of the multiplication of cells in plants by division, and therefore we are by no means inclined 

 to agree with Professor Kolliker, as to the rarity of this form of cell-multiplication in die 

 vegetable kingdom, nor, consequently, in what he says at the conclusion of the preceding 

 note. All botanists of any note (Nageli, Von Mohl, Hoffmeister, Alex. Braun, Schacht, Hen- 

 frey) maintain at the present time, that the process of cell-division so far from being "rare,"' 

 is that which occurs in by far the great majority of cases in plants. " That the formation 

 of cells, in all organs of plants (except the cells originating in the embryo sac), depends 

 upon the division of older cells, is an opinion, whicli could not for a long time past be op- 

 posed by any carefid observer, unless he were misled by preconceived notions.' (Von 

 Mohl, "Anatomy and Physiology of the Vegetable Cell,'' 1851, Henfrey's translation). Nor 

 can we agree with Professor Kolliker's estimate of the relative frequency of occurrence and 

 importance of endogenous cell-development and cell-division in the animal world. In young 

 cartilage, which is cited by our author as a locality in which endogenous cell-development 

 takes place, we must afllrm, on tlie contrary, that the process is as much one of cell-division 

 as it is in any plant. At this perioil the so-called " nuclei" of the cartilage completely fill 

 their cavities (c. g. nasal cartilage of four months' foetus), and may be seen in all stages of 

 division. The walls of the cavities grow in, pari passu, and eventually form a partition 

 between the two nuclei, or rather primordial utricles, which have been thus developed from 

 one. 



Remak, who, in a very valuable paper (Ueber die Entstehung der Bindegewebes und 

 Knorpels, Mull. Archiv, 1852), has advocated this view, so far as cartilage and connective- 

 tisue are concerned, does not appear to have seen the necessity of extending it to the other 

 tissues. As Reichert, however, long since pointed out (see note, § on Connective Tissue) 

 whatever determines the nature of the cartilage corpuscle, and of its matrix, determines that 

 of all the other tissues whose anatomical continuity with cartilage can be traced directly or 

 indirectly. Thus a direct anatomical continuity may be shown to exist between the matrix 

 of cartilage, the apparent fibrilhe of cennective tissue, the librilkeof muscle, the homogeneous 

 matrix of the cutis and of its papilke, and the so-called walls of the epithelial cells; while 

 a perfect identity in size, structure, and relation, may be traced between the corpuscles of 

 cartilage, the "nuclei" of connective tissue, those of muscle, of the papillae and of the epithe- 

 lial cells. — Tes.] 



