164 



PROTOZOOLOGY 



without reversion to a double form. It is probable that the organ- 

 ism showed a long-lasting modification, but there was no con- 

 stitutional change in the organization of the animal. Jollos 

 (1913-1934) observed that Paramecium, when subjected to 

 various environmental influences, such as high temperature, 

 arsenic acid, etc., showed variations which were gradually lost, 

 although lasting through one or more periods of conjugation and 

 endomixis, and that if the organisms were subjected to environ- 

 mental changes during the late phase of conjugation, certain 



Fig. 81. Chilodonella uncinata (MacDougall). a, b, ventral and 

 side view of normal individual; c, d, ventral and side view of the tailed 

 mutant. 



individuals, if not all, become permanently changed. Possibly 

 here one sees that the reorganizing nuclear material has been 

 affected in such a way that the hereditary constitution or geno- 

 type has become altered. 



MacDougall subjected Chilodonella uncinata to ultraviolet rays 

 and produced many changes which were placed in three groups: 

 1) abnormalities which caused the death of the organism; 2) tem- 

 porary variations which disappeared by the third generation; 

 and 3) variations which were transferred unchanged through 

 successive generations, hence considered as mutations. The 

 mutants were triploid, tetraploid, and tailed diploid forms (Fig. 

 81), which bred true for a variable length of time in pure-line 

 cultures, either being lost or dying off finally. The tailed form dif- 

 fered from the normal form in the body shape, the number of 



