MORPHOGENESIS 787 



does not imply that fifty or eighty diminutive regenerators can be ob- 

 tained from the original cell. In uninucleate types, only one such frag- 

 ment may be obtained. It is also apparent that parts of the original 

 derived organization, cortical organelles, oral structures, and so forth 

 are not requisite for the survival and regeneration of the smallest frag- 

 ments. The requirements are primarily qualitative: a representative bit 

 of the basic protoplasmic organization. The matter of obtaining a viable 

 nucleus or fragment of the macronucleus has had much to do with the 

 values so far determined. 



6. THE NUCLEI IN REGENERATION 



More than a century after Rosel (1755) distinguished ecto- and endo- 

 plasm in amoebae by surgical methods, the works of Brandt (1877), 

 Nussbaum (1884), and Gruber (1886) inaugurated an era of active 

 interest in protozoan physiology. Although not in general agreement as 

 to the sensory and reactive capacities of enucleated fragments, these 

 investigators, together with Balbiani (1888), Verworn (1888, 1892), 

 Hofer (1890), Lillie (1896), Prowazek (1904), Popoff (1907), and 

 many others, showed that both nucleus and a certain amount of cyto- 

 plasm are essential for the continuation of the vegetative, reproductive, 

 and reparative activities of the cell. The consensus of these early publica- 

 tions is aptly stated by Minchin (1912) : "Non-nucleated fragments may 

 continue to live for a certain time; in the case of amoeba such frag- 

 ments may emit pseudopodia, the contractile vacuole continues to pulsate, 

 and acts of ingestion and digestion that have begun may continue; but the 

 power of initiating the capture and digestion of food ceases, consequent- 

 ly all growth is at an end, and sooner or later all non-nucleated bodies 

 die off" (p. 210). 



There still exists a diversity of opinion regarding the essential nature 

 of the nucleus or dimorphic nuclei in regenerative or regulative func- 

 tions. Apropos of the latter, Moore (1924) places a greater premium 

 than most upon ultimate physiological recovery: 



In general previous investigators have centered their attention upon morpho- 

 logical regeneration alone, and have considered the restoration of external 

 organelles as sufficient evidence of a completion of the process. Since form 

 regulation in the Protozoa is of little value if not accompanied by the ability 

 to continue normal existence, it would appear that a more valuable definition 



