222 INTERCELLULAR SUBSTANCE. 



substance. In very old cells, the small portion of bioplasm 

 still unconverted into formed material, dies, and the cell 

 having by this time arrived at the surface, is cast off, a 

 mass of perfectly passive, lifeless, almost dry formed 

 material. 



The facts here described are illustrated in fig. i, PI. V, 

 p. 220, which should be carefully studied. 



Of the so-called Intercellular Substance. In cartilage 

 and some other tissues, there is no line of separation 

 between the portion of formed material which belongs to 

 each bioplast, as is the case in epithelium, but the formed 

 material throughout the entire tissue forms an uninterrupted 

 mass of tissue, matrix, or, as it has been termed, connective 

 substance. (PI. VI, fig. 3). From the apparent essential 

 difference in structure, it has been supposed that tissues of 

 this character were developed upon a principle very different 

 from that upon which epithelial structures were produced. 

 It has been maintained by some that in cartilage a cell-wall, 

 distinct from the intervening transparent material, existed 

 around each cell, and it has been very generally concluded 

 that the matrix was deposited between the cells, altogether 

 independently of the living matter of the cell. Hence this 

 was called " zwfcr-cellular substance." 



But it must not be supposed that epithelium is in all 

 cases to be distinguished from cartilage by the existence of 

 separate cells. In many forms of epithelium at an early 

 period of development, the formed material corresponding 

 to the several masses of bioplasm is continuous throughout, 

 and presents no indications of division into separate cells. 

 This is well seen in the lower part of the specimen repre- 

 sented in PI. V, fig. i, but in fig. 2, PI. VI, an unusually 



