MORPHOGENESIS 



Regeneration and Division 



797 



The lines of investigation summarized by Calkins (1934) and in 

 part by Dixie Young (1939) predicate an increase of vitality through 

 reorganizational processes in division, encystment, endomixis, and conju- 

 gation. The de- and redifferentiation incident to the physiological ("spon- 

 taneous") and reparative types of regeneration provide other opportuni- 

 ties for the renovation of derived structures. If we are correct in the 



Figure 182. Divisional and physiological reorganization in Uronychia. Sister cells 

 operated on four hours after division. Five hours after injury, the cell cut as shown in A 

 regenerated by dividing. Physiological reorganization without division occurred in B 

 after the same time interval. (Modiiied from Dembowska, 1926.) 



belief that nuclear and cytoplasmic reorganization stimulates vitality, 

 then regeneration in the strict sense includes not only the replacement 

 of a part but also some degree of rejuvenescence of the whole cell. Is it 

 a priori a beneficial process? At least it is one which can be provoked 

 artificially. 



To what extent are reproduction and regeneration dependent upon the 

 same fundamental activities of the cell? Gruber (1886), Morgan 

 (1901), Dembowska (1926), Causin (1931), and M. E. Reynolds 

 (1932) have remarked that the initial steps in division and regenera- 

 tion are comparable. Since the ends achieved by these processes are 



