22 



CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



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 functions. 



Line of division "^| 



of cells. 



Antipole of daughter ' 

 nucleus. 



Remains of spindle. 



"'--> Lighter substance 

 --'~"" of nucleus. 



Cell protoplasm. 

 Hilus. 



FIG. 1 8. Final Stages of Karyokinesis. In the lower figure the changes are still more 

 advanced than in the upper. (Waldeyer.) 



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 

 pressure 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 



FIG. 19. Karyokinesis, Mitosis, or Indirect Cell Division (diagrammatic). A, Cell 

 with resting nucleus; B, wreath, daughter centrosomes and early stage of achromatic 

 spindle; C, chromosomes; D, monaster stage, achromatic spindle in long axis of nucleus, 

 chromosomes dividing; E, chromosomes moving toward centrosomes; F, diaster stage, 

 chromosomes at poles of nucleus, commencing constriction of cell body; C, daughter nuclei 

 beginning return to resting state; H, daughter nuclei showing monaster and wreath; 7, 

 complete division of cell body into daughter cells whose nuclei have returned to the resting 

 state. (After Bohm and von Davidoff.) 



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 



