380 



GRACE MEDES 



from solutions e and / at 72 hours and 98 from e at 96 hours. 

 The same features characterize these specimens except that 

 here fusion of the individual rods in the arms has been almost 

 complete. 



All these figures are characterized by a high degree of sym- 

 metry. This quality is evident, even in those cultures where 

 skeletons have been reduced to the extent indicated in figure 

 95. In the presence of an excess of carbonate, then, in contrast 



Fig. 96 lie, figure 97 11/, 72 hrs.; figure 98 lie, 96 hrs. Complete disap- 

 pearance of Na characters and appearance of CO3. 



to the other experimentally altered media, asymmetry is not 

 correlated with inhibition of growth. 



The most pronounced effect of addition of acids or alkahes 

 to the medium in which the Arbacia eggs are developing is the 

 decrease or increase in rate of growth. As shown in the ac- 

 companying experiments, acid invariably produces a retarding 

 and inhibiting effect; alkalies, in small amounts, cause an ac- 

 celeration of growth in early stages, resulting in increased size. 

 In later stages, however, these same cultures show a retarda- 

 tion of the rate of development so that ultimately they lag 



