HIGHER RIGID SUPPORTING TISSUES 69 



cells with large nuclei and small cytoplasmic bodies that are fairly com- 

 pact but yet send out numerous branches which anastomose with one 

 another. The deposition of the cartilage substance, called the matrix, 

 begins at the principal boundary of the cytoplasmic body, and the ma- 

 terial first appears as a thick rim of a hyaline substance surrounding 

 each cell. These rims coalesce with each other and new concentric 

 layers are laid down, always next to the cell and by the agency of its 

 cytoplasm. The material of the matrix changes in chemical reaction 

 as it grows older, and in some forms of cartilage the concentric layers of 

 which it is composed are plainly visible. Usually they are not so unless 

 by special treatment under the microscope. 



In most cartilages, and especially in that of the squid, which we are 

 studying, the layers of matrix do not entirely shut in the cell. The pro- 

 cesses of the cytoplasm pass through them and unite with the similar pro- 

 cesses from other cells, thus forming pathways from cell to cell through 

 the matrix, for the passage of food and other materials which are carried 

 by the protoplasmic processes. 



As the cartilage grows, its cells multiply in order that there may 

 always be enough 

 cells scattered 7r ~~~~^? : i?^^ 

 through the matrix ' 



to have full control 



of its growth, sup- ^,^ m x_ /*>,- 



port, or atrophy at 'jjpLi -\ .A . V '- fe- :/ H/..' : . 

 all times. This " 



multiplication is by 

 mitosis, although 

 amitosis possibly 

 occurs in later 



growth processes FIG. 71. Cartilage of an adult squid. Intercellular canals partly 



(Fig. 71), and when shown, x 650. 



the two daughter 



cells are completed, they continue the formation of the matrix as 



before, from every part of the surface of their cell bodies. 



This results in the formation of a thin but growing plate of the matrix 

 between them, which is continued. As several divisions usually occur 

 in succession, the cells are often found arranged in groups of two, four, 

 or eight, as in Figure 71. The cartilage cells store glycogen, and when 

 prepared for the microscope are usually shrunken by the loss of this 

 glycogen, which readily dissolves in the fluids used to harden the tissue. 

 This simple cartilage is one of a large group of tissues of which there 

 are several kinds. 



The simplest kind is that just described, and is known as a hyaline 



