230 



PROTOZOOLOGY 



were inherited through successive generations and hence considered 

 as mutations. The mutants were triploid, tetraploid, and tailed 

 diploid forms (Fig. 96), which bred true for a variable length of time 

 in pure-line cultures, either being lost or dying off finally. The tailed 

 form differed from the normal form in the body shape, in the number 

 of ciliary rows and contractile vacuoles, and in the mode of move- 

 ment, but during conjugation it showed the diploid number of chro- 

 mosomes as in the typical form. The tailed mutant remained true 

 and underwent 20 conjugations during ten months. 



Fig. 96. Chilodonella uncinata (MacDougall). a, b, ventral and side 

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



Kimball (1950) exposed Paramecium aurelia to beta particles from 

 plaques containing P 32 and obtained many clones which multiplied 

 more slowly than normal animals or died, which conditions were 

 interpreted by him to be due to mutational changes induced in the 

 micronuclei by the radiation. Kimball found that the radiation was 

 less effective if given just before the cytoplasmic division than if 

 given at other times during the division interval and that exposure 

 of the organisms to ultraviolet ray of wave length 2537 A inactivates 

 the Kappa (p. 239). 



The loss of the blepharoplast in trypanosomes mentioned above 

 occurs also spontaneously in nature. A strain of Trypanosoma evansi 

 which had been maintained in laboratory animals for five years, sud- 

 denly lost the blepharoplast (Wenyon, 1928) which condition re- 

 mained for 12| years (Hoare, 1940). Hoare and Bennett (1937) found 

 five camels out of 100 they examined infected by the same species 

 of trypanosome that was without a blepharoplast. One strain inocu- 

 lated into laboratory animals has retained this peculiarity for nearly 



