CELLS. 71 



I). The elastic fibres, fibrous networks, and fibres. 



c. The fibres of connective [areolar] tissue, the nctivorks of connective 

 tissue (reticulated connective tissue), and the membranes composed of 

 connective tissue (homogeneous connective tissue). 



d. The transversely striated muscular fibres and muscular fibre net- 

 ivorks. 



e. The nerve-fibres and nerve-fibre networks. 



f. The capillary plexuses of the blood-vessels and lymphatics. 



g. The trachese and tracheal plexuses of the invertebrata. 



All these higher elementary parts possess essentially the same proper- 

 ties as cells, especially growth in length and thickness, absorption, 

 metamorphoses, and excretion, an^ to some extent contractility ; to- 

 gether with other functions which may perhaps also be demonstrated in 

 cells. Their growth is manifested by the fact, that all, without excep- 

 tion, are much shorter and narrower immediately after their formation 

 than subsequently ; their absorptive powers, by the dependence of their 

 functions upon the circulation, by the phenomena of resorption in the 

 lymphatics and blood-vascular capillaries, and by the above-mentioned 

 growth, which can only take place by the reception of substances into 

 their interior. A metamorphic and an excretive power must be assumed 

 to exist in them ; it is testified by the well-known peculiar products of 

 decomposition of the muscles, and also by the continual transmission 

 of blood-plasma through the walls of the capillaries. The muscular 

 fibrils possess contractility, and the processes in the nerve-fibres, though 

 very peculiar, and at present not to be defined more nearly, may 

 nevertheless in some respects be compared to the functions of the nerve- 

 cells. 



With regard to the trachese, which are placed here only for complete- 

 ness' sake, I long since found that their terminations are formed by the 

 coalescence of stellate cells into tubes, in which the original cell-contents 

 either remain or become developed into a spiral fibre ; and I published 

 a concise notice of the fact in the year 1849 (" Zeitschrift fiir wiss. 

 Zool.," Bd. i. p. 215, Anmerkung), a view which has since been con- 

 firmed by H. Meyer (Ibid. Bd. i.), and more recently by Leydig (Ibid. 

 Bd. lii. Heft 4.) 



Literature of the Elementary Parts. — In addition to Schwann's work 

 quoted above, may be named: Kolliker, "die Lehre von der thierischen 

 Zelle," in Schleiden u. Niigeli's " Zeitschrift fiir wiss. Botanik.," Heft 

 ii. 1845; Remak, " U eber extracellulare Entstehung thierischen Zellen 

 und die Vermehrung derselben durch Theilung u. Uber Entstehung des 

 Bindegewebes u. d. Knorpel," in Mailer's " Archiv," 1852, i. (Xo longer 

 available. Bcmak assumes quite confidently, what I only indicated, that 

 animal cells have a primordial utricle, without giving any demonstration of 



