28o J. F. McClendon 



and started separate cultures from them, which were kept for 

 months. In every case the progeny of one individual showed a 

 curve of as little spread as those given of P. caudatum. Thus it 

 was possible to obtain a culture of minute individuals or one of 

 giants or one of medium size. Subjecting a culture to higher tem- 

 perature or increased salinity decreased the size of the individuals 

 while lower temperatures increased the size of the individuals. 

 P. aurelia of this region must then be dimorphic or else it hap- 

 pened that in starting both the above cultures {e and /) only large 

 and small and no medium sized individuals were procured. Large 

 samples of water containing decaying leaves, etc., from various 

 places developed no cultures of Paramoecia, so that more data 

 for aurelia was not obtained. We may say then that aureha 

 differs from caudatum in the presence of two micronuclei and 

 that some aurelia are smaller than the smallest caudatum. 



It has frequently been noted that conjugating individuals are 

 smaller than non-conjugants. I think that the fact that the 

 mouths of conjugants are closed is sufficient to cause the smaller 

 size. By comparing curve c (of individuals fed less) with curve 

 d (of individuals fed more) you may note that those fed less are 

 smaller. However, no matter how little food is given Paramoecia 

 they can still take in water through the mouth and be swelled up 

 with vacuoles, which is not the case with conjugants. Note that 

 the variation of the well fed individuals is greater than that of the 

 poorly fed. Dr. Pearl ('07) found the same to be true of non- 

 conjugants as contrasted with conjugants. 



In conclusion, a note on the effect of a certain food may be of 

 interest. It is well known that hay infusion has to be often re- 

 newed to keep a culture of Paramoecia in good condition. If the 

 culture is left in the same infusion the individuals become smaller, 

 sluggish and finally die. However, if a considerable amount 

 of cane sugar be added to the culture, the Paramoecia are very 

 little affected at first but after several weeks become more active 

 and live for months. Whether this be due to alcohol that appears 

 or to bacteria produced in the culture was not determined. 



