THE TYPICAL CELL 



FlG. 6. ClLIATE AND FLAGELLATE CELLS. 



A, ciliated cells isolated from the 

 trachea of a cat ; , human spermatozoa 

 ./, in surface view ; 2, in profile. Ex- 

 amined fresh in normal saline solution, 

 x 550. 



It may be reticular, alveolar, or homogeneous ; it may also con- 

 tain fibrillae of considerable length, either straight or coiled, which 

 may even be continued through the exoplasm and into adjacent 

 cells. 



The nucleus is also subject to 

 great variations in size, in shape, 

 and in the arrangement of its 

 chromatic fibrils. These changes 

 are in great measure dependent 

 upon the processes of karyoki- 

 nesis. 



As a result of the processes of 

 cell multiplication, which begin 

 with the germ cell, new tissue cells 

 are formed, which exist either as 

 isolated cells, in relation with their 

 neighbors by contact only, or as 



a continuous protoplasmic mass or syncytium, which is formed by 

 fusion of the exoplasm of adjacent cells (Studnicka *). The true 

 syncytium is usually found in embryonic tissues ; the mature tis- 

 sues, on the other hand, possess a distinctly cellular character. 



The differentiation of cells in the course of development results 

 in the formation of special tissue groups, the protoplasm of each 



group presenting certain common char- 

 acteristics. These tissue groups form 

 the primary tissues of the body. Thus 

 we distinguish : (1) epithelial tissues, (2) 

 connective tissues, (3) muscular tissues, 

 (4) nervous tissues, (5) blood, (6) lymph. 

 Still further differentiation may occur 

 within each group. Thus, for example, 

 connective tissue may be fibrous, elastic, 

 areolar, reticular, cartilaginous, bony, etc. 

 These changes, apparently taking place 



The connective tissue inclosed / 



by the syncytium contains under the influence of the nucleus, are 

 three capillary vessels. Hema- more pronounced at the periphery of the 

 cell. The most marked protoplasmic dif- 

 ferentiation is therefore found in the exoplasm it results in the 

 formation of cilia, intercellular bridges, and the fibrillae of epithe- 



FlG. 7. A VILLUS OF THE HU- 

 MAN PLACENTA, SHOWING A 

 PERIPHERAL SYNCYTIUM OF 

 IRREGULAR THICKNESS. 



*Anat. Anz., 1903. 



