202 W. V. LAMBERT, W. S. RICE, AND H. C. A. WALKER. 



Polytoma culture. Race B continued to the 209th generation 

 and C to the 43rd, without apparent loss of vigor, when the 

 experiment was discontinued. The entire history of the two 

 races, A and B, may be seen in Fig. 1. These two races started 

 from two sisters and their rate of reproduction was determined 

 at seven different periods ranging over about 13 months. For 

 some unknown reason Race B showed a lower rate of reproduction 

 at the first count, but at the second count the rate had risen 

 above that of Race A, and furthermore, in all the subsequent 

 counts, covering about a year, it remained above the rate of Race 

 A. Toward the end the two rates began to diverge considerably 

 due to the gradual weakening of Race A while Race B maintained 

 its former rate of reproduction. 



Conclusions. 

 From the fact that the A race died out before the 200th 

 generation it is obvious that some unexpected influence must 

 have entered, most probably poor food, since other cultures of 

 Hydatina senta have reproduced four and five hundred genera- 

 tions parthenogenetically. Therefore, our results can hardly be 

 called conclusive, but the opinion seems to be justified that the 

 constitutional vigor of the A race, fed upon an exclusive colorless 

 diet, was noticeably weakened, while that of the B race, fed 

 upon a diet of Polytoma plus a green food containing carbo- 

 hydrates, was sustained and even raised above that of the 

 wild races. If this is true, as it certainly seems to be, it would 

 appear that the decline in vigor and eventual death in the 

 races observed by Shull and Whitney was due to an unbalanced 

 diet, rather than to the parthenogenetic method of reproduction, 

 as they concluded. 



Zoological Laboratory, 



University of Nebraska, 

 Lincoln, Nebraska, 

 June 1, 1922. 



LITERATURE CITED. 



Calkins, Gary, N. 



'04 Studies on the Life History of Protozoa. Journal of Experimental Zoology, 

 Vol. I. 

 Castle, W. E., F. W. Carpenter, A. H. Clark, S. O. Mast, and W. M. Barrows. 



