External Factors and Size 



137 



breadth, representing a mean decrease of twenty per- 

 cent in body volume. 



Similar but more marked results were found by Jen- 

 nings ('08b) upon Paramecium in cultures of single 

 clones. The organisms were largest when taken from 

 new cultures, gradually diminishing in size as the cul- 

 tures aged. When transferred from old cultures to 

 new ones, restoration of the full original size occurred 

 in one or two days (table 12). 



Table 12. 

 Effect of Food and of Age of Culture Upon the Dimensions of Para- 

 mecium. Clone D, Second Series. Data of Jennings ('08b.) 



The progressive changes of size in ageing mass cul- 

 tures of Colpoda (figure 42) and of Stylonychia (figure 

 43) were measured by Enriques ('09). The diminu- 

 tions of size were irregular, perhaps depending upon 

 the reflourishing of food organisms in the first two 

 weeks of culture. 



In cultures of Colpidium it was noted by Wachen- 

 dorff ('12) that mean body length declined during four 

 weeks from about 200 micra to about 50 micra. 



A more complete analysis of the ageing of Colpid- 

 ium cultures was made by Vieweger ('25), who fol- 

 lowed the changes of size in clonal mass cultures. The 

 relative densities of population were simultaneously 

 measured (figure 44). An important result was that 

 the size decreased very markedly some days before re- 

 production ceased. The progression of this decrease 



