8 GARY N. GALKINS 



may become P. aurelia, and P. aurelia may in time lapse again 

 into P. caudatum. It is to be inferred from this that the various 

 forms which have been described as P. aurelia are in reality only 

 "sports" of P. caudatum, and if such " sports" are unable to keep 

 up by inheritance the characteristic structural differences which 

 distinguish them from the ancestral form, although this is main- 

 tained for the long period of 45 generations, they cannot be 

 considered a "good species." On the other hand, R. Hertwig 

 gives some evidence, not conclusive, however, to show that P. aure- 

 lia, after conjugation, reorganizes with two micronuclei. 



It must be admitted that one experience of this kind may be 

 insufficient to throw out a species that has appeared to be so well 

 established. It may be that my observation was made on a chance 

 abnormality which paralleled P. aurelia, and that the real P. aurelia 

 retains its integrity as a species. Personally, however, I do not 

 believe it, and am reasonably confident that such abnormalities 

 may be of frequent enough occurrence in nature to account for the 

 numerous descriptions of P. aurelia that have been given. Forty 

 generations is a long series for an abnormality to be transmitted, 

 and the number of individuals represented by 2 to the 4oth 

 power (as my culture represents), allowing for natural loss through 

 enemies, etc., would provide enough specimens with this abnor- 

 mality to justify the belief that it is normal. On the other hand, 

 it cannot be stated that P. aurelia is a well-established species. It 

 is relatively rare in nature; its specific character has been con- 

 tested by such eminent authorities as Biitschli, Engelmann, Bal- 

 biani, Stein, Koelliker, and Gruber; while Maupas and Hertwig 

 succeeded in establishing it as a species only on the slender basis 

 given above. My one experience with this culture is strong enough, 

 as I believe, to reanimate the old skepticism, and to justify us in 

 abandoning either P. aurelia or P. caudatum. The latter is the 

 more recent name given by Ehrenberg, and according to the rules 

 of priority must be replaced by Paramecium aurelia, the name applied 

 by O. F. Miiller to the "slipper animalcule." 



The physiological features presented by this experiment give 

 some interesting data upon the vitality and nuclear relations. The 

 curve shows that a sudden rise in vigor accompanied the return 



