160 On the Genetics of the Ciliate Protozoa 



78. The two species of Paramecium called avreiia and caudatum 

 differ fioin one another, inter alia, in that the former has two micro- 

 nuclei, the latter one. [See Maupas (1.S88, 1889), Hertwig (1889).] 

 Calkins (1906), however, advanced the view that both forms belong to 

 the .same species. Of a pair of exconjiigants of caudatum. (1 micro- 

 nucleus) he found that one reorganized after conjugation as a caudatum 

 form, the other as an aurelia — with 2 micronuclei. The aurelia form 

 persisted for a number of generations, but finally reverted t(j the 

 caudatum type. Jennings and Hargitt (1910) and Woodruff (19116) 

 nevertheless regard aurelia and caudatum as " good " species. In this 

 I agree, and I think the conclusions of the former explain Calkins's 

 results — " in rare cases specimens of the caudatum. races have two 

 micronuclei, those of aurelia, races but one'." 



79. It may be noted here that Sun (1912) has observed divisions 

 in Paramecium in which the nuclei arc abnormally distributed — the 

 daughter-nuclei all remaining in one individual whilst the other receives 

 none. Enucleate and supernucleate forms may thus arise. The foi-ma- 

 tion of similar enucleate Stentojs has been observed by Prowazek (1904). 

 Individual Paramecia containing only a micronucleus have been found 

 by Kasanzeff (1901) and Sun (1912). The former found them in starved 

 cultures, and believed that they arose by an irregular division or 

 through " hunger degeneration " of the meganucleus. No evidence 

 of the production of new races in this fashion has yet been brought 

 forward. 



80. Abnormally nucleate races oi' Paramecium have, however, been 

 experimentally produced by Lewin (1910). By cutting an individual 

 transversely through the meganucleus, he obtained two organisms, one 

 of which retained the micronucleus whilst the other had none. The 

 latter continued to divide, thus producing an " amicronucleate " race. 

 In another case, Lewin cut an abnormally dividing organism so that 

 one-half contained a meganucleus only, the other a meganucleus and 

 both daughter-micronuclei. The former gave rise to an "amicronucleate" 

 race — multiplying slowly, but normally : the latter produced a race with 

 two micronuclei. Both bred true for a considerable time-. 



' It is perhaps worth noting here that Powers and Mitchell (lOlll) have described what 

 appears to be another species of Paramecium (called P. multimicroniu-leutuin) which re- 

 sembles candatum but possesses from 2 to 7 micronuclei. 



■^ Le Dautec (1897) had previously stated that ciliates deprived of their micronuclei by 

 cuttinK in this manner are able to regenerate this organ. A full account of his experiments 

 has never been published, nor has any confirmation of his statements yet appeared. 



