100 GENERAL PRINCIPLES OF ZOO LOG Y. 



the chief role, in the latter, on the contrary, their impor- 

 tance is subordinate to the plasmic products, the "inter- 

 cellular substances" which chiefly determine the character 

 of the various kinds of connective tissue. 



Function of Connective Tissue. The primary func- 

 tion of connective tissue is to fill up the spaces in the in- 

 terior of the body between the various organs, thereby 

 uniting together not only the single parts of the organs, 

 but also the various organs themselves. In consequence of 

 this, the connective substances contribute to the firmness of 

 the joints, and are correspondingly employed in the building 

 up of the skeleton. To accomplish this, substances which 

 usually have a greater firmness than protoplasm are formed 

 on the surfaces of the cells, and, since they are included 

 between the cells, these are called intercellular substances. 

 In proportion as the intercellular substance increases in 

 volume the cells themselves diminish and become incon- 

 spicuous corpuscles, the connective-tissue corpuscles, or, as 

 seldom happens, entirely disappear. Since in the con- 

 nective tissues the intercellular substances are most impor- 

 tant, it is readily understood that the distinctions between 

 the various kinds of connective tissue rest chiefly upon the 

 differing constitution of this intercellular substance. The 

 following forms are to be distinguished: (i) cellular con- 

 nective tissue; (2) homogeneous connective tissue; (3) 

 fibrous connective tissue ; (4) cartilage ; (5) bone. 



Cellular Connective Tissue is least distinctly stamped 

 with the characteristics of the group. It derives its name 

 from the fact that the cells in it make up the chief mass, 

 while the cell-products are present only in their incipiency. 

 The cells are large vesicular bodies which have secreted a 

 firm though thin covering representing the intercellular 

 substance. Many such cells surrounded by a membrane 

 are closely pressed together after the manner of vegetable 

 cells and become flattened polygonally (Fig. 36). 



Homogeneous Connective Tissue. In the case of 

 homogeneous connective substance the intercellular substance 



o 



is usually present in considerable quantity as a glassy, 



