110 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-celis, 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 followimg 
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- 
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