104 CLAUDE W. MITCHELL 



were placed in cultures containing a moderate supply of Para- 

 mecia. They ingested these organisms until their stomachs be- 

 came noticeably distended. This was followed by a slight in- 

 crease in the size of the individuals over those in less favored 

 cultures and also by an increase in the number of simultaneously 

 developing embryos, as many as eight or ten being sometimes 

 counted. But these young were not as large, when born, as 

 were those born of parents that contained but one or two. This 

 latter fact is doubtless a mere consequence of the larger number 

 produced at one time; the smaller young were, however, healthy 

 and developed into normal saccate individuals, showing no ten- 

 dency toward transition. 



Excessive food 



To a number of cultures Paramecia were added until the medi- 

 um became an almost milk-colored broth. The rotifers, however, 

 did not thrive under these conditions; their all but empty digestive 

 tracts indicated that little food was eaten, and they assumed a 

 vertical position in the fluid, with their coronas open wide against 

 the surface. Even when returned to normal medium this new 

 reaction was repeatedly manifested for a period of four to five 

 hours. This experiment, therefore, did not accomplish its aim; 

 the results indicated a general decrease in metabolism. 



Effects of low nutrition and starvation 



An individual was isolated in the normal amount of culture 

 medium which had, however, been filtered. To this was added 

 the smallest number of Paramecia which experiment had indi- 

 cated would serve for the minimum food supply capable of main- 

 taining life and at the same time some rate of reproduction. 

 Such young as were born were immediately isolated in like cul- 

 ture media. Under these conditions the total number of young 

 decreased in each generation, until in the fifth but one was pro- 

 duced. The same conditions, continued to the ninth generation, 

 showed similiar low rates of reproduction. Upon resuming a 

 normal food supply in the ninth generation (table 5) a normal 



