TRANSFORMATION OF BRACHIONUS PALA INTO B. AMPHICEROS. 119 



observed and only one possessed the posterior lateral spines. If 

 the Chlamydomonas contained sodium silicate the rotifers in 

 using them for food ought to have obtained enough of it with 

 which to have formed the additional spines. When, however, 

 the Chlamydomonas were transferred from the siliceous medium 

 to the medium free from sodium silicate the siliceous materials 

 which their bodies may have contained may have diffused out 

 into the general medium, thus leaving their bodies practically 

 free from the siliceous materials and consequently having no 

 effect upon the rotifers. 



It is, of course, quite possible that the siliceous material is 

 not used at all in the formation of new spines and the increase 

 in size of the other spines but that the sodium silicate, in some 

 unknown way, stimulates each organism so that it takes out of 

 the water more skeletogenous building material of another kind 

 than under normal conditions. As yet, it is not known that the 

 skeleton contains any siliceous material but it is considered to 

 be entirely of chitinous material. If this is true the effect of 

 sodium silicate upon the rotifers in causing an increase in the 

 number and size of their spines is certainly not clear. 



The fertilized eggs that were produced by the spined females 

 of the Brachionus amphiceros type in the cultures containing 

 sodium silicate produced females of the Brachionus pala type 

 entirely lacking the lateral posterior spines of their mothers. 

 278 fertilized eggs from such mothers were allowed to develop 

 and none of the females that they produced possessed the addi- 

 tional spines. Sachse and Powers found also that the fertilized 

 eggs of the polymorphic females which they observed always 

 developed into females of one particular type. 



SUMMARY. 



1. Socium silicate added to the culture medium in which the 

 rotifer Brachionus pala was living caused nearly all and in many 

 cases caused all of the descendants to form two additional 

 posterior lateral spines and also to increase the size of the other 

 spines thus forming Brachionus amphiceros. 



2. The parthenogenetic eggs from females reared in sodium 

 silicate solutions developed into young females of the Brachionus 



