26 



COMPARATIVE ANATOMY. 



kinds that connective tissue is richer than any other in the various 

 phenomena of differentiation. 



§ 22. 



4) Cartilaginous tissue is characterised by cells lying in a 

 firmer intercellular substance. Its cells do not, except in a few cases, 

 possess distinct processes, or processes which can be easily made 

 out ; but are very nearly circular in form, or else oval or fusi- 

 form. The amount of intercellular substance varies in amount. 

 It is distinguished from those forms of connective tissue which are 

 formed of simple cells placed in a homogeneous intercellular sub- 

 stance, by its greater rigidity. Cartilaginous tissue is well adapted by 

 the possession of this character to function as an organ of support. 

 When the cells predominate, and there is but little intercellular 

 substance, and when what there is is in the form of fine membranes, 

 cartilage is seen to be directly allied to vesicular connective tissue. 

 The protoplasm of these cells often takes on a definite arrangement, 

 and forms bands which extend from the nucleus to the periphery, 

 and unite together there. They are separated from one another by 

 spaces which contain fluid (Fig. 9). In proportion as its intercellular 

 substance is diminished, does this tissue differ more and more from 



ordinary cartilaginous tissue. In the 

 protoplasm of cells of this kind, which 

 are found forming a sort of skeleton 

 in the Medusas, the phenomenon of 

 streaming of the protoplasm may be 

 seen. 



If the intercellular substance in- 

 creases, it either remains homogeneous 

 (hyaline cartilage), or it undergoes 

 further differentiations like those of 

 connective tissue ; but these differentiations do not much affect its 

 relations to its cells. When the intercellular substance breaks up 

 into fibres, we get fibrous cartilage; when elastic nets appear 

 in it we get elastic cartilage. By gradual changes of the inter- 

 cellular substance, as well as of the cells, cartilaginous tissue passes 

 into fibrous connective tissue, and thus indicates its close connection 

 with that form of tissue. The cells also become more specially modified 

 in some cases by being elongated or producing radiating processes, 

 which unite with those near them : as, for example, in many Selachii, 

 or more developed still in many Cephalopoda. The intercellular 

 substance then appears to be traversed by the processes from the 

 cells (Fig. 10). The phenomenon, which in the cases just cited is 

 greatly exaggerated, obtains also in ordinary hyaline cartilage, 

 where the cells are apparently sharply marked off from one another ; 

 for the intercellular substance may be seen to be traversed by 

 processes, although these are, of course, extremely fine. 



The intercellular substance of cartilaginous tissue is always 



Fig. 9. Cartilage cells from the 

 tentacle of a Medusa (Cunina). 



