HO FIBRE-CELLS, ETC. 



principle is the basis both of the organized and unorganized 

 tissues. We shall have further evidence of this presented to 

 us in the following classes, which comprise the rest of the 

 tissues, — those, indeed, which are most perfectly organized, 

 and the most important to the animal organism. In them 

 we shall also find that the formation of cells is the general 

 principle of development, and that their elementary particles 

 are derived from cells, although at the first glance one would 

 scarcely imagine that any connexion could exist between them 

 and cells. 



CLASS IV. 



Fibre-cells, or tissues, which originate from cells that become 



elongated into bundles of fibres. 



Mere fibres are all that can be detected as the elementary 

 components of the tissues of this class when they are examined 

 in the mature animal. But when we investigate the mode in 

 which they are generated, we see that the fibres are formed 

 only as prolongations of cells, which, in most instances, are 

 elongated in two opposite directions, sometimes terminating 

 at once in a fasciculus of fibres, at other times in a single fibre, 

 which afterwards splits into several finer ones. This con- 

 stitutes the characteristic feature of the class. We are already 

 acquainted with the type of the prolongation of cells into fibres 

 in the pigment -ramifications, osseous corpuscles, &c. The 

 cells next to be considered differ from them in the following 

 particulars : the fibres originating from any one cell generally 

 lie together in a fasciculus, and in these prolongations of the 

 cells, it is principally the wall which is most strongly developed, 

 whilst, in the former instances, the cells though extended into 

 fibres, were chiefly rendered conspicuous by their cavities. 

 This class comprises the Cellular (areolar), Fibrous, and Elastic 

 tissues. 



1. Cellular [areolar) Tissue. This tissue is known to be 

 composed of extremely minute, tough, smooth fibres, having 

 a pale outline, and usually a serpentine course ; they 

 may be seen in their natural state in the mesentery with- 



