PROTOZOA : RHIZOPODA. 



45 



little spherical masses of sarcode which may be derived from 

 the nucleus by fission, or may be produced by a segmentation 

 of the endosarc, the animal having previously become torpid, 

 and the nucleus and contractile vesicle having disappeared. 

 These little masses, however produced, develop themselves 

 when liberated into ordinary Amosbce. This last method of 

 reproduction is obviously very closely analogous to the pro- 

 duction of ' pseudonavicellas ' in an encysted Gregarina. 



The remaining members of the Amoebea are constructed 

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

 the nearly allied Dtfflugia 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 (Jig. 26). In 

 Arcella there is a discoid or bason-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 

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

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

 ai/iinalcule (Actinophrys sol) is another well-known Rhizopod 

 which is usually placed in this order (fig. 3). It consists of 

 a spherical mass of sarcode, about 11,300 of an inch in dia- 

 meter, and usually covered with long, radiating, filamentous 

 pseudopodia, which are 

 much less mobile than in 

 the case of the Amoeba. 

 The division of the sub- 

 stance of the body into ec- 

 tosarc and endosarc is to- 

 lerably evident, and the 

 latter contains numerous 

 granules and vacuoles. The 



pseudopodia are derived Fig. S.Actinophrys tol: showing the radiating 



from the ectosarc alone, the j^gm?*" ne specimen has 8waUowed 

 endosarc not passing into 



them, and they exhibit a circulation of granules along their 

 edges, though this is not nearly so marked a feature as in the 

 case of the Foro/minifera. A nucleus and contractile vesicle 

 are also present. 



The Amoebea may be divided into two sub-orders : 1. Amoe- 

 bina, including those forms which have the body naked ; and 

 2. Arcellina, comprising those in which the body is protected 

 by a carapace. 



