324 BOBERT T. HANCE 



VIII. DISCUSSION 



In the course of some experiments by Dr. M. H. Jacobs on the 

 effect of high temperatures on paramoecia, various lots of these 

 animals were ejected into hay infusions at temperatures ranging 

 from about 36° ot 42°C. Those that survived this treatment 

 were thrown into a battery jar containing hay infusion. In this 

 jar the new animals were discovered. I am still of the opinion 

 (stated in my preliminary note in Science (2) ) that these new 

 paramoecia may have been produced as the result of the high 

 temperature, although I have been unsuccessful as yet in a 

 number of attempts to reproduce this race artificially. It 

 would be a most striking coincidence if this multi-vacuoled char- 

 acter has been in existence for any length of time that its dis- 

 covery should be delayed until found in the culture made up of 

 the descendents of heat treated animals. ^ 



In this new paramoecium we have a form which lends itself 

 to a study of the processes of heredity in the protozoa. The 

 character is seemingly not at all comparable to those reported 

 for Difflugia by Jennings (5). Since the vacuoles are, however, 

 very definite structures and a marked variation from the com- 

 mon form, their study and comparison is exceedingly interest- 

 ing and offers many possibilities. The data possessed at pres- 

 ent are insufficient to make a discussion of these hereditary 

 processes of value. Selection experiments, though incomplete, 

 seem to indicate as far as they have been carried that the char- 

 acter cannot be affected by selection in either direction. It 

 will be impossible to determine whether the tendency or poten- 

 tiality for extra vacuoles is germinally controlled until we have 

 succeeded in crossing the two strains. There is some evidence 

 at present that points to the cytoplasm as the portion of the cell 



2 Since this paper was sent to press I have received Shumway's paper (11) 

 in which he has reported the formation of extra contractile vacuoles in thyroid 

 fed animals. None of his specimens had more than three vacuoles and the in- 

 heritance of the extra vacuole in the form studied has not been demonstrated. 

 The percentage of extra-vacuoled animals among his thyroid fed paramoecia 

 (20 to 30 per cent) is considerably less than I have found in my race (77 per 

 cent). 



