MORPHOGENESIS 781 



ing species (undescribed) of Euplotes. The fact that E. patella regener- 

 ated very well under the same conditions led her to the conclusion that 

 "under identical conditions there is a difference in the regenerative 

 power of these two races of Euplotes" (p. 353). It should be noted that 

 none of the undescribed species survived the operations; all distinte- 

 grated during or immediately after the operation. 



Of particular merit is the work of Tartar (1939), in which rigid 

 criteria were set up for distinguishing between recovery and regenera- 

 tion and between form restoration and complete regeneration. Twenty- 

 five races, representing seven species, were used in the experiments to 

 determine whether there are racial or specific differences in the regenera- 

 tive ability of Paramecium. A total of 865 anterior transections were 

 performed, in 509 of which the organisms survived. Morphological and 

 complete physiological regeneration occurred in 98 percent of the sur- 

 vivals. Having established from minor operations the working hypothesis 

 that "any Paramecium able to recover from the injury of cutting is able 

 to regenerate completely" (p. 196), Tartar performed operations of a 

 more serious character — excisions involving the major portion of the 

 posterior end — upon five races of P. caudatum. Complete regeneration 

 occurred in 93 percent of the 121 survivals. According to these results, 

 the ability of Paramecium to regenerate is much greater than previous 

 investigations have shown and, furthermore, the regional differences in 

 individuals of the same species are relatively slight. The final conclu- 

 sion that there is no racial nor species variation in regeneration of cells, 

 even after quite severe cuts, may be subject to further qualification. Al- 

 though the compiled data show no large order variations in the incidence 

 of regeneration among the different species or races of Paramecium, 

 there remains the possibility of genetic differences in the capacity for 

 regeneration after repeated injuries or in the rate of regeneration. 



4. DEGREE OF INJURY AND REORGANIZATION 



In many Protozoa the extent of cytoplasmic dedifferentiation varies 

 with the degree of injury; but is does not necessarily follow that a small 

 or even a large operation will be followed by complete resorption and 

 reintegration of the cell structures. In holotrichs, Loxophyllum for exam- 

 ple (Holmes, 1907), the mode of restoration may be simple and direct, 

 with the alteration of uninjured, preexisting parts reduced to a minimum. 



