434 



ROBERT W. HEGNER 



(fig. 1), was begun on March 21, and its original progenitor 

 lived throughout the rest of the period, giving rise in that time 

 to ten offspring. Specimens from branches of this family that 

 had been constantly subjected to the sodium silicate solution 

 were at intervals transferred to the normal culture medium, but 

 in every case the size, spine number, and spine length character- 

 istic of the parent line were immediately regained. Family 14 

 was continued until it contained 135 members and included 

 specimens of the eighteenth generation, but no heritable variations 

 were noted that could be attributed to the changed medium. 

 Figures 4 and 5 illustrate the changed condition of the offspring 



?-87(8) 



-18-87(8) 



^12-27(e)- 



Fig. 2 Arcella dentata. 

 see figure 1. 



Part of the pedigree of family 15. For description 



when the parents of this family and of family 15 were subjected 

 first to the sodium silicate solution and later were replaced in 

 the normal medium. 



c. Color of the shell 



Another character that was modified by the presence of sodium 

 silicate was the color of the shell. Arcellas that are reared in a 

 normal medium have a shell that is at first almost transparent, 

 but gradually changes to a pale yellow, and in time becomes a 

 very deep brown. The offspring reared from parents that were 

 kept in the sodium silicate solution were pale yellowish green, in 

 color, as long as they remained in this medium, but became of the 



