CELLS. 71 



b. The elastic fibres, fibrous networks, and fibres. 



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

 works. 



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



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



g. The tracheae 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, and 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 tracheae, 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 fur 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. iii. Heft 4.) 



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

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

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

 ii. 1845; Remak, " Ueber extracellulare Entstehung thierischen Zellen 

 und die Vermehrung derselben durch Theilung u. liber Entstehung des 

 Bindegewebes u. d. Knorpel," inMuller's "Archiv," 1852, i. (No longer 

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

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



