EFFECT OF CONJUGATION 355 



immediate production of strongly marked heritable differences 

 by conjugation. 



The data of our present experiment, given in tables 34 and 35, 

 bring to light many other important relations, which will be 

 dealt with in subsequent papers. For our present purposes it is 

 sufficient that the experiment demonstrates that conjugation 

 produces within a pure race heritable differentiations; so that as 

 a result races diverse in their heritable characters arise from a 

 single race with uniform heritable characters. 



Our previous experiments had shown that conjugation increases 

 variation; and that the variations observed to follow conjugation 

 are heritable. The present experiment puts the finishing touch 

 on this demonstration by showing that these heritable variations 

 do not arise without conjugation.^ Thus we find that one method 

 of producing new strains is by conjugation. 



We have now in hand the essential facts for drawing conclusions 

 as to the actual effects of conjugation on the stock. 



IV. RESUME OF RESULTS: DISCUSSION, AND CONCLUSIONS 



In the foregoing sections are detailed the results of a large 

 number of experiments in which conjugants were compared with 

 non-con jugants of the same stock and the same cultural history. 

 Wliat effects do we find conjugation to produce? 



The prevailing view as to the effects of conjugation is that it 

 produces rejuvenescence in the stock. This view is excellently 

 stated in Calkins' recent Protozoology ('09), particularly in chap- 

 ter III. The essentials are somewhat as follows: 



If we could take such an entire succession of cells thus formed from 

 the repeated divisions of a fertilized protozoon, and if at any given 

 period could combine them in one mass of cells, we should have the 

 analogue of a metazoon and would find that the protoplasm represented 

 by the agregate of cells would manifest the same successive periods of 

 vitality as those of youth, adolescence, and old age in Metazoa. We 

 would find that the young cells divided more rapidly than they do later 

 in the cycle; we should find that after a certain time they become 

 sexually mature and are able to conjugate and so to perpetuate the 



2 There remains the possibilty that heritabh' variations of a totally different 

 (lesser) order of magnitude may arise duriiiji; vegetative reproduction. 



