VARIATION AND HEREDITY 



229 



Jennings (1941) outlined five types of long-lasting inherited 

 changes during vegetative reproduction, as follows: (1) changes that 

 occur in the course of normal life history, immaturity to sexual ma- 

 turity which involves many generations; (2) degenerative changes 

 resulting from existence under unfavorable conditions; (3) adaptive 

 changes or inherited acclimitization or immunity; (4) changes which 

 are neither adaptive nor degenerative, occurring under specific en- 

 vironmental conditions; and (5) changes in form, size, and other 

 characters, which are apparently not due to environment. 



Whatever exact mechanism by which the long-lasting modifica- 



Fig. 95. a-c, Uroleptus mobilis (Calkins) (a, a pair in conjugation; b, 

 an individual from the third generation by division of a double organism 

 which had been formed by the coalescence of a conjugating pair; c, a 

 product of reversion); d, a double animal of Euplotes patella (Kimball). 



tions are brought about may be, they are difficult to distinguish 

 from permanent modification or mutation, since they persist for 

 hundreds of generations, and cases of mutation have in most instan- 

 ces not been followed by sufficiently long enough pure-line cultures 

 to definitely establish them as such (Jollos, 1934; Moewus, 1934; 

 Sonneborn, 1947). 



Jollos observed that if Paramecium were subjected to environ- 

 mental change during late stages of conjugation, certain individuals, 

 if not all, become permanently changed. Possibly the recombining and 

 reorganizing nuclear materials are affected in such a way that the 

 hereditary constitution or genotype becomes 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) temporary variations 

 which disappeared by the third generation ; and (3) variations which 



