August 4, 1911] 



SCIENCE 



137 



divides equally as though the cell were 

 perfect, hence the posterior cell has a re- 

 duced cytoplasm and a full size nucleus, 

 or the ratio N/P is changed to the ad- 

 vantage of the nucleus. Nevertheless, this 

 cell, in some cases at least, grows and di- 

 vides again without regenerating the lost 

 part and a second abnormal division (/) 

 results in a second abnormal cell and a 

 normal cell. Ultimately, however, the ab- 

 normality is lost and the normal form re- 

 gained. Here, something more subtle than 

 mass relations is at work and we are justi- 

 fied in looking for important results from 

 the further study of protozoa along these 

 experimental lines. 



4. Regeneration. — The power of regen- 

 eration of the cell, also, is much less ex- 

 tensive than we were led to believe by the 

 early experiments of Balbiani, Verwom, 

 Gruber, Hofer, Prowazek and others. It 

 seemed to follow from their experiments 

 that any frag-ment of a protozoan, pro- 

 vided it contained some nuclear material, 

 would regenerate quickly into a normal 

 cell. Lillie showed that a piece as small 

 as one twenty-seventh of the original ani- 

 mal would develop into a normal Stentor. 

 The power to regenerate, however, varies 

 not only in different races of the same 

 species of protozoa, but also in the same 

 cell at different inter-divisional ages. In 

 four different races of Paramecium cau- 

 datum I have found that in one race only 

 about one per cent, regenerated after cut- 

 ting; in another about 10 per cent, regen- 

 erated; in a third race about 30 per cent, 

 and in a fourth about 90 per cent. Here, 

 then, is a well-marked racial difference in 

 respect to regeneration. 



Again, if we cut the large hypotrichous 

 eiliate TJronycliia transfitga just after di- 

 vision, both fragments will contain parts 

 of the macronueleus, but only the micro- 

 nucleus-holding fragment will restenerate. 



If cut from six to eight hours after divi- 

 sion the result is the same, although the 

 non-regenerating fragment livas for days. 

 But if we cut the cell just prior to cell di- 

 vision, both fragments regenerate perfectly 

 except for the absence of a micronucleus 

 in one. The power to regenerate, there- 

 fore, varies in the same cell from a mini- 

 mum just after divLsion to a maximum 

 just prior to division, a phenomenon lend- 

 ing support to the view that certain stuffs 

 are accumulated during cell life up to a 

 condition analogous to saturation, when the 

 reaction follows, in this case regenerative 

 processes. With such activity the accu- 

 mulated stuff is used so that regeneration 

 does not follow mutilation immediately 

 after, or for some time after, cell division. 

 Certainly the generalization that nucleated 

 fragments of protozoa will regenerate is not 

 well founded. 



Similarly with other early generaliza- 

 tions. The classic experiments of Maupas 

 seemed to prove that "Weismann's theory 

 of the potential immortalitj' of protozoa 

 was wrong. Later research confirmed 

 ilaupas in the main, iintil to-day Weis- 

 mann's theorj', in its original form at 

 least, is untenable, protozoa having the 

 same potential of immortality that metazoa 

 have, no more and no less. Later research, 

 however, has given highlj' variable results 

 in studies of the life history, and again 

 we find an individuality in different races 

 of the same species. Woodruff's remark- 

 able and enigmatical results with Parame- 

 cium caudatum, for example, show that 

 earlier conclusions and generalizations 

 were premature. 



One general conclusion, however, seems 

 to be weU. established, viz., that the proto- 

 zoon's life history runs in cycles of asex- 

 ual and sexual phases. The beautiful work 

 of Schaudinn in 1899, on the life cycle of 

 Coccidium scJnibergi, gave the model fol- 



