MODES OF CELL CONNECTION 21 



The Cell Types. All of the elementary tissues consist of cells and 

 of their altered equivalents. It will be as well therefore to indicate some of the 

 differences between the cells of the body. They are named in various ways, 

 according to their shape, origin, and junctions. 



From their shape, cells are described as spherical or spheroidal, which is the 

 typical shape of the free cell; this may be altered to polyhedral when the pres- 

 sure on a mass of cells in all directions is nearly the same; of this the primitive 

 segmentation cells afford an example. The discoid form is seen in blood- 

 corpuscles, and the scale-like form in superficial epithelial cells. Some cells 

 have a jagged outline and are then called prickle cells. Cells of cylindrical, 

 conical, or prismatic form occur in various places in the body. Such cells may 

 taper at one or both ends into fine processes, in the former case being caudate, 

 in the latter fusiform. They may be greatly elongated so as to become fibers. 



...-. Remains of spindle. 



Line of division --^^?T7>r r -'-"'r^^VA ""** Lighter substance 

 of cells. """ of nucleus - 



Antipole of ^^^^^mWl ______ Cell protoplasm. 



nucleus. MllllWwmJfcl^J/Jlllf 



---- Hilus. 



FIG. 19. Final Stages of Karyokinesis. In the lower figure the changes are still more ad- 

 vanced than in the upper. (Waldeyer.) 



Cells with hair-like processes, or cilia, projecting from their free surfaces, are 

 a special variety. The cilia vary greatly in size, and may even exceed in length 

 the cell itself. Finally, cells may be branched or stellate with long outstanding 

 processes. 



From their function cells are called secreting, protective, sensitive, contractile, 

 and the like. 



From their origin cells are called epiblastic and mesoblastic and hypoblastic 

 (ectodermic, mesodermic, and endodermic). 



Modes of Cell Connection. Cells are connected together to form 

 tissues in various ways. 



They are connected by means of a cementing intercellular substance. This 

 is probably always present as a transparent, colorless, viscid, albuminous 

 substance, even between the closely apposed cells of epithelium; while in 

 the case of cartilage it forms the main bulk of the tissue, and the cells only 

 appear as embedded in, not as cemented together by, the intercellular substance. 

 This intercellular substance may be either homogeneous or fibrillated. In 

 many cases, e.g., the cornea, it can be shown to contain a number of irregular 

 branched cavities, which communicate with each other, and in which branched 



