22 SIMPLE RHIZOPODS. PART in. 



presents various degrees of piano-convexity, the con- 

 vexity in some cases amounting to a hemisphere. They 

 rarely, if ever, have mineral matter on their surface, 

 which is studded with regular but very minute hexa- 

 gonal reticulations. The aperture or mouth of the 

 shell is small, and invariably occupies the centre of the 

 plane surface, its margins being more or less inverted. 

 The form of the shell is exceedingly varied, sometimes 

 it even has horns indefinite in number, sometimes sym- 

 metrical, sometimes not ; when its test or covering be- 

 comes too small for its increasing size, it quits it, and 

 secretes a new one. The filamental pseudopodia proceed 

 from the mouth of the shell only, and by means of these 

 it creeps about on its mouth in search of food. 



Fig. 95. Simple Rhizopods. A, B, Difflugiae ; C, D, Arcellse. 



The Difflugia build their own shells, which are usually 

 truncated spheres, ovate, or sometimes elongated into 

 the form of a pitcher or flask. The most minute recog- 

 nisable of these shells is about the . A - ^ 00 of an inch in 

 diameter, but they are constructed with the most perfect 

 regularity. The Difflugia pyriformis or symmetrica has 

 the form of an egg with an aperture at the small end. 

 It is entirely made up of rectangular hyaline plates, 

 arranged with the greatest regularity in consecutive 

 transverse and longitudinal rows, the smaller ones being 

 at the extremities, while the larger ones occupy the 

 central and widest portion of the structure. The inhabi- 

 tant of this abode is an Amoeba with a sarcode body 



