124 MICROSCOPY FOR BEGINNERS. 



is followed by another and another, until the shell is 

 raised and moved slowly away. 



There are several species of the genus Difflugia, of 

 which the following are about the commonest. They 

 are found abundantly in the mud and among Sphagnum. 



1. Shell pear-shaped (Fig. 97), without spines, although 



the summit may be prolonged into one or two 

 points ; usually formed of sand-grains, 

 sometimes with adherent diatoms ; oc- 

 casionally formed entirely of diatoms ; 

 mouth at the narrow end, circular, 

 smooth, without teeth or lobes. The 

 body within the shell is usually green, 

 sometimes colorless ; pseudopodia col- 

 orless, thick, blunt. It is almost as 

 fond of the cell contents of Spirogyra 

 as is Yampyrella, and obtains them in a similar way ; 

 but instead of appearing to suck them out of the 

 cell, Difflugia jpyriformis pierces the wall, inserts 

 its pseudopodia, with them surrounding the color 

 bands and other cell contents, lifts the whole out 

 and passes it into the body within the shell. I have 

 seen a single Difflugia empty four Spirogyra cells 

 in succession. This species is common. Difflugia 

 pyriformis, Fig. 97. 



2. Shell nearly spherical, with from one to twelve, usu- 



ally three or seven, pointed spines arranged in a 

 circle around the upper part, and formed of sand- 

 grains. These spines are hollow, and communicate 



