EFFECTS OF REORGANIZATION 351 



An exceptional case of mutation is that of Chilodon uncinatus 

 described by MacDougall (1925). 



A single individual of Chilodon uncinatus was isolated by 

 MacDougall (1925) in December. Its progeny were maintained 

 in pure line cultures until lost in June. In May, larger forms 

 appeared in the cultures and these increased until they out-num- 

 bered the smaller forms, few of which could then be found. Cyto- 

 logical examination showed that the larger form was morphologically 

 identical with the smaller form, with the exception of the micro- 

 nuclei in which the chromosomes were eight in number as against 

 four in the smaller form. MacDougall worked out the meiotic divi- 

 sions for both types and found a similar history in both (Fig. 149, 

 p. 299) and correctly interprets the tetraploid form as a mutant 

 from the ordinary diploid type. 



The entire matter of heredity in Protozoa, together with rejuven- 

 escence and related problems have been fully treated in a remark- 

 ably frank and impartial manner by Jennings (1929) in his excellent 

 monograph on the Genetics of the Protozoa, to which the reader is 

 referred. 



The Protozoa, finally, cannot be regarded as simple organisms 

 which may be permanently changed in structure or function at will. 

 Each type has a remarkable tenacity of life which we believe is 

 organization and its activity, and which may be temporarily modi- 

 fied by environmental changes, but in which permanent changes 

 are rare, and when they occur must come apparently from within. 

 Organization, on the one hand, is continuous and has been handed 

 down from the indefinite past to the species which we know today. 

 Vitality, on the other hand, may be discontinuous and variable and 

 is manifested by the sum of activities which take place in the 

 organization at any time. Death is not of necessity the cessation 

 of vitality but the disintegration of the organization after which 

 vitality is impossible. 



