72 GENERAL ANATOMY OF THE TISSUES. 



the fact; he ascribes the multiplication of cells by division to be widely 

 extended through embryonic tissues ; finds (what others will not 

 easily succeed in doing) two membranes in the later cleavage-masses, 

 and wrongly, denies altogether the occurrence of free cell-development) ; 

 also the treatise of Donders, cited below under the head of elastic tissue ; 

 and the embryological monographs of Reichert, Bischoff, Vogt, Remak, 

 and myself. Inasmuch also, as the doctrine of the vegetable cell is impor- 

 tant for zoologists, I call attention to Schleiden's first treatise (" Ab- 

 handlung liber die Bildung d. Pflanzenzelle," Mull. "Arch.," 1837); to 

 his " Elements of Botany ;" to Nageli's Essay " Ueber die Pflanzenzelle," 

 in the "Zeitschrift flir wissenschaftlich. Botanik," Heft ii. ; and to 

 Mohl's monograph upon this subject, in Wagner's " Handworterbuch" 

 (" Mohl on the Vegetable Cell," translated by A. Henfrey, London, 

 1852). [To these should be added the important monographs of 

 Schleiden, " Beitriige zur Phytogenesis," in Muller's Archiv, p. 137; 

 of Rosenthal, " De formatione granulosa in nervis aliisque partibus 

 organismi animalis," Vratislavire, 1837 ; of Kramer "Bemerkungen liber 

 das Zellenleben in der Entwickelung des Froscheies" in Mliller's Archiv, 

 1848, and the more recent works of Dr. Schacht, on the " Vegetable 

 Cell" (Die "Pflanzenzelle") Berlin, 1852 ; and of Alex. Brown on 

 "Rejuvenescence" (Verjllngung), Leipzig, 1851. — DaC] 



III. OF THE TISSUES, ORGANS, AND SYSTEMS. 



§ 20. The elementary parts of both the simpler and the higher kinds, 

 are not dispersed irregularly in the body, but are united according to 

 determinate laws, into the so-called tissues and organs. Under the 

 first denomination comes every constant arrangement of the elementary 

 parts always recurring in similar modes in the same parts ; under that 

 of an organ, on the other hand, a certain sum of elementary parts of a 

 definite form and function. When several or many organs of a similar 

 or diff"erent kind are united into a higher unity, this is called a system.. 



The tissues are of diff"erent kinds, according as structural elements of 

 one kind only occur in them, or as various elements and even organs 

 take part in their formation. We can thence distinguish simple and 

 complex tissues, which, however, cannot be sharply separated from one 

 another, and which may be most fittingly arranged in the following 

 series : — 



{a.) Simple tissues. 



1. Epidermic tissue. 



2. Cartilaginous tissue. 



3. Elastic tissue. 



4. Connective tissue.* 



* [Fibrous tissue, see note, p. 47. — Ed.] 



