8 EiriZOPODA. 



certain degree of consistence, so as to serve as an 

 envelope for the protection of the softer sarcode 

 within. But in Difflugia we find it invested with 

 a membranous 'carapace' or 'lorica/ of an oblong 

 or oval figure, from the terminal aperture of which 

 the pseudopodia are protruded {^fig. 2, d). In 

 Arcella the carapace assumes a discoid or hemi- 

 spherical form {fig. 2, c), with the single narrow 

 orifice placed on its flat surface. In both of these 

 Khizopods the surface of the carapace often ex- 

 hibits tubercles or depressions, or has particles 

 of sand, &c., imbedded in its substance ; and in 

 Arcella the margin is frequently provided with 

 long spinous prolongations. The curious Pam- 

 phagus, described by Bailey, would seem to form 

 a connecting link between these Ehizopods and 

 Amoeba. Like the latter, it is destitute of a cara- 

 pace, but it agrees with Arcella and Difflugia in 

 having the pseudopodia protrusible from one ex- 

 tremity only of the body. It undergoes the most 

 extraordinary mutations of form, which are chiefly 

 the result of its habit of swallomng almost every 

 substance with which it comes in contact. Hence 

 the appropriate name (P. niutabilis) conferred on 

 this Ehizopod by its late discoverer. 



4. €lassi@catl€»ia of MMzopoda The Ehi- 



zopoda may be arranged under two sections, 

 Amoebea and ForarYiinifera. The first of these 

 may be again subdivided into two minor groups : 

 I. Amoebina, including those Ehizopods which 

 have the body naked, viz. Amoeba, Actinophrys, 

 and Pa7)iphagus ; and 2. Arcellina, which con- 

 tains Difflugia and Arcella. All these Ehizopods 



