ENVIRONMENT ON ARCELLA 



429 



food conditions constant when undertaking experiments involv- 

 ing division rate. They also prove that Arcella dentata is 

 able to grow and reproduce under adverse conditions with 

 respect to the food supply, but at a much less rapid rate. 



b. The effects of underfeeding upon the diameter of the shell 



The offspring of parents that were underfed showed the effects 

 of this treatment immediately, being smaller than their parents 

 in every case. When these offspring were underfed, they like- 

 wise gave rise to smaller offspring than the normal for the line, 

 but not, on the average, smaller than themselves. When, on 

 the other hand, these small offspring of underfed parents w^ere 



TABLE 1 



Arcella dentata. Table showing the distribution in diameters (in units of 4-3 m) 

 of specimens in families, 2, 3, and 4 during periods when they were being reared 

 in normal medium and when they were underfed 



returned to normal cultural conditions, their first offspring 

 showed the effects of the abundance of food, becoming close to 

 the normal. Also, when full-sized specimens that were produced 

 under normal conditions and which had given rise to small off- 

 spring when subjected to underfeeding, were again supplied with 

 an abundance of food, the size of their offspring immediately 

 attained that normal for the line. The six cases on following 

 page present data characteristic of the series. 



Table 1 gives the distribution of the diameters of the speci- 

 mens reared in families 2, 3, and 4, both when the parents were 

 in normal cultural conditions and when underfed. The following 

 means bring out the significance of these data : 



