GENERAL PRINCIPLES OF ZOOLOGY. 



proportion as the intercellular substance increases in volume the 

 cells themselves diminish and become inconspicuous corpuscles, 

 the connective-tissue corpuscles, or, as seldom happens, entirely 

 disappear. Since, in the connective tissues, the intercellular sub- 

 stances are most important, it is readily understood that the dis- 

 tinctions between the various kinds of connective tissue rest chiefly 

 upon the differences of this intercellular substance. The following 

 forms are to be distinguished: (1) cellular connective tissue; (2) 

 homogeneous connective tissue; (3) fibrous connective tissue; (4) 

 cartilage; (5) bone. 



Cellular Connective Tissue shows the characteristics of the 

 group least distinctly. It owes its name to the fact that the cells 

 make up the chief mass, while the cell-products are inconsiderable. 

 The cells are large and vesicular bodies which, like plant cells, are 

 closely pressed together and are consequently polygonal (fig. 38). 

 They have secreted between them a firm but thin layer of inter- 

 cellular substance. 



FIG. 38. Cellular connective substance. 

 Cross-section through the notochord 

 of a newly hatched Trout. 



FIG. 39. Homogeneous connective sub- 

 stance of Sycandra raphantu. (After 

 F. E. Schulze.) 



Homogeneous Connective Tissue. In the case of homogeneous 

 connective substance the intercellular substance (or matrix) is 

 usually present in considerable quantity as a transparent mass, 

 nearly invisible under the microscope, sometimes soft like jelly, 

 often firmer (fig. 39). The gelatinous cells lying in it are either 

 spherical or send branching processes into the matrix. Such 

 processes may unite to form meshes which, like a pseudopodial 

 network, unite cell to cell. Frequently the matrix contains, in 

 addition, isolated firm fibres or threads, which, on account of 



