PROTOZOA ; RHIZOPODA. 



57 



The remaining members of the Amazbce 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. 3, 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. Difflugm often exhibit the 

 phenomenon known as " conjugation " or " zygosis." Under 

 these circumstances, two Difflugite come in contact ; the mouths 

 of the two tests are brought together ; the two animals flow back- 

 wards and forwards into each other's tests, with an apparently 

 complete incorporation ; and finally they separate again, and 

 each retires to its own test. In Arcella there is a discoid or 

 basin-shaped carapace, secreted by the animal itself, and like- 

 wise 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 body, 

 the remainder of the surface appearing to be of too resistant 

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

 (Actinophrys sol) is another well-known Rhizopod which is 



Fig. 5. Actinofhrys sol : showing the radiating pseudopodia. 

 One specimen has swallowed a Diatom. 



usually placed in this order (fig. 5). It consists of a spherical 

 mass of sarcode, about 1-1300 of an inch in diameter, and 

 usually covered with long, radiating, filamentous pseudopodia, 

 which are much less mobile than in the case of the Amceba. 

 The division of the substance of the body into ectosarc and 

 endosarc is tolerably evident, and the latter contains numerous 



