72 



PALMER : 



FIGITRE I. 



Experiment II. — A fresh mount was made from the same 

 gathering and left in darkness upon the stage for two hours, 

 with momentary and slight exposure to light every half hour. 

 At the end of that time the movements of the Naviada; and 

 some small forms of Nitzschia were as vigorous as ever. The 

 slide, with the diatoms in it, was now put into a dark box for 

 twenty hours, or until the next evening. It was then arranged 

 on the stage with practically no exposure to light. After an 

 interval of half an hour of darkness, the diaphragm was 

 opened slightly. The Naviculce had all come to rest, but the 

 numerous minute Nitzxchicr were moving with vigor. The 



