A PliELIMIXARY STUDY OF THE FIXER STRUCTURE 

 OF ARCELLA 



JOSEPH A. CUSHMAN AND WILLIAM P. HENDERSON 



This study of Arcella is based upon two species, Arcella vulgaris 

 Ehrenberg and Arcella mitrata I^eidy. The structure of the test 

 in Arcella is usually described as given by Leidy ("Fresh-water 

 Rhizopods of North America," U. S. Geol. Surv. Territories, vol. 

 12, p. 167): "Composed of a more or less translucent or trans- 

 parent chitinoid membrane, with a minutely hexagonal cancellated 



magnification shows furihcr coinplicaiion ot tlii- stniciuro, not 

 797 



