ENVIRONMENT ON ARCELLA 435 



normal brown color as soon as they were transferred to normal 

 cultures. The color mechanism of Arcella seems to be very 

 sensitive to environmental factors. During the work on selection 

 it became evident that pure lines probably exist with respect to 

 the length of time it requires for the young to reach their defin- 

 itive color and also with regard to the intensity of the color 

 attained. Changes in the character of the food were likewise 

 found to affect the color. For example, when food was obtained 

 from vegetation taken from a cement tank in the botanical garden 

 on the Johns Hopkins University campus, the offspring became 

 dark brown almost immediately after fission; specimens reared 



?-20(s)fo)(l): 



.9-24 (n ) f 1 ) 9-25 (n ) (1 ) 



^9-23(n)fl) 9.23(n)(l) 



~^8-23 E 

 • 11-27 (n) 



- 8-85(n) 10-29fn) 



Fig. 3 Arcella dentata. Complete pedigree of family 26. For description 

 see figure 1. 



in hay infusions were more yellowish in color than normal, and 

 those fed on material collected from a spring-water fish pond at 

 Cold Spring Harbor, Long Island, were characteristically pale. 



Arcella thus resembles the many other organisms that are 

 modified by changes in the environment ; they remain so as long 

 as they are in this environment, but return to their former con- 

 dition when transferred back to the original medium. 



THE ADDITION OF ALCOHOL 



One of the substances to which Protozoa have been found to 

 be resistant is alcohol. Experiments were begun to determine 

 the effects of alcohol on Arcella dentata, but were terminated 



