n6 



DAVID D. WHITNEY. 



elapsed observations were made on the rotifers in these jars 

 which at this time contained many thousands. In the control 

 jars free from sodium silicate only three females from nearly 



B 



FIG. 2. A, adult female reared in culture medium free from sodium silicate; 

 B, adult female reared in culture medium containing sodium silicate. 



six thousand females possessed the posterior lateral spines while 

 in the jars containing sodium silicate many of the females pos- 

 sessed the posterior lateral spines. In some of the jars containing 



