No. 479] 



FINER STRUCTURE OF ARCELLA 



799 



drawn away until its level was so reduced that air reached the 

 specimen. Bubbles at once formed in some of the cancelli and 

 were present after dehydrating, clearing, tearing in pieces, and 



chambers lying l)etween 

 them. That there is })ut 

 one membrane is very 

 strongly indicated by the 

 present study. 



The next thing to deter- 

 mine was the position of the 

 single membrane, whether 

 it is on the outer or the inner 

 side of the network. In the 



wo thin plates, with the cancellated 

 ?rtwig and Lesser thought. If there 

 I be impossible, by the simple method 

 bubbles to form in the closed 



