CYTOMORPHOSIS. 15 



cytes and the superficial cells of the bladder the cell bodies of which often 

 fail to divide following the division of their nuclei. Thus cells with two 

 or more nuclei may be produced by amitosis. It occurs in wounded 







- ' 



Beginning Completed Beginning Completed 



Division of the nucleolus. Division of the nucleus. 



FIG. 17. AMITOSIS IK EPITHELIAL CELLS FROM THE BLADDER OF A MOUSE. X 560. 



tissues where it has been interpreted both as a result of injury and as 

 evidence of activity toward repair. In the egg tubes of certain insects 

 amitosis is a common and normal process. 



CYTOMORPHOSIS. 



Cytomorphosis is a comprehensive term for the structural modifications 

 which cells or successive generations of cells may undergo from their 

 origin to their final destruction. It implies that the life of a cell is limited, 

 and that during its life it may change in structure by becoming differentiated 

 or adapted to the performance of special functions, and that finally it will 

 pass through regressive changes to its death. Successive generations of 

 cells may represent stages along a certain line of differentiation. The 

 cells resulting from mitotic division begin their specialization where the 

 parent cell left off, and the phenomena of regression are then reserved 

 for the final generations in the series. Four successive stages of cytomor- 

 phosis have been recognized: First, the undifferentiated stage; second, 

 that of progressive differentiation; third, the stage of regression; fourth, 

 the removal of dead material. These may be considered in turn. 



Undifferentiated cells, as can be seen in sections of young embryos, 

 are characterized by large nuclei and relatively little protoplasm. They 

 have great power for undergoing division. The subsequent increase 

 of cytoplasm which makes functional differentiation possible, retards the 

 rate of mitosis. In the adult, relatively undifferentiated cells are found 

 in many situations, as, for example, in the deep layer of the epidermis. 

 These cells are a source of supply to replace the outer cells as they differ- 



