PROTOZOA: RHIZOPODA. 



49 



when liberated into ordinary Amoeba. This last method of 

 reproduction is obviously very closely analogous to the pro- 

 duction of " pseudonavicellae " in an encysted Gregarina. 

 It has been doubted, apparently with considerable reason, 

 whether the so-called Amcebce are distinct species of animals, or 

 whether they are not rather transitory stages in the life-history 

 of other organisms. It is quite certain that several of the 

 Protozoa pass through an Amoeboid stage, and it is also certain 

 that vegetable matter not uncommonly assumes similar char- 

 acters (e.g., the mycelium of certain fungi). It is therefore 

 not impossible that the forms known to the microscopist as 

 Amoeba may be ultimately discovered not to be permanent and 

 distinct species ; but the evidence on this head is still de- 

 fective. 



The remaining members of the Amoebea are constructed 

 more or less closely after the type of the Amoeba itself. In the 

 nearly allied Difflugia the sarcode forming the body of the 

 animal is invested with a membranous envelope or " carapace," 

 strengthened by grains of sand and other adventitious solid 

 particles, and having a single aperture at one extremity, 

 through which the pseudopodia are protruded (fig. 2, b\~ The 

 animal generally creeps about head-downwards, so to speak ; 

 that is to say, with the closed end of the carapace elevated 

 above the surface on which it is moving. In Arcella there is a 

 discoid or basin-shaped carapace, secreted by the animal itself, 

 and likewise possessing but a single pseudopodial aperture, 

 placed in this case on the flat surface of the body. 



In Pamphagus there is no carapace, but the pseudopodia 

 are nevertheless protrusible from one extremity only of the 



Fig. 3. Actlnophrys sol: showing the radiating pseudopodia. 

 One specimen has swallowed a Diatom. 



body, the remainder of the surface appearing to be of too 

 resistant a consistence to allow of this. The common sun- 

 animalcule (Actinophrys sot) is another well-known Rhizopod 



VOL. I. D 



