PROTOZOA: AMCEBEA. 



developed into a fresh Amoeba. Thirdly, by the production 

 of 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 Amoeba. This last method of 

 reproduction is obviously very closely analogous to the pro- 

 duction of " pseudonavicellae " in an encysted Gregarina. 



The remaining members of the Amcebea are constructed more or less 

 closely after the type of the Amceba 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 hav- 

 ing a single aperture at one extremity, through 

 which the pseudopodia are protruded (fig. 

 9). 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. 

 Difflitgice often exhibit the phenomenon 

 known as " conjugation " or " zygosis." 

 Under these circumstances, two Difflugice 

 come in contact ; the mouths of the two tests 

 are brought together ; the two animals flow 

 backwards and forwards into each other's 

 tests, with an apparently complete incorpora- 

 tion ; 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 likewise possessing 

 but a single pseudopodial aperture, placed in 

 this case on the flat surface of the body. One 

 species of Arcella (viz., A. arenarid) is ter- 

 restrial in its habits. 



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. Cochliopodiiim 

 is like Arcella, but the test is quite flexible. 



Pseiidochlamys, Hyalosphenia, Quadrula, &c., are other fresh- water Rhizo- 

 pods more or less closely allied to Arcella and Difflugia, but often ex- 

 hibiting interesting and remarkable modifications of structure. 



The Amoebea may be divided into two sub-orders : i. Amct- 

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

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

 by a carapace. The latter are included by Hertwig and Lesser 

 along with Gromia and the typical Foraminifera in a common 

 group, to which they give the name of Thalamophora. The 



E 



Fig. 9 . Difflugia pyriformis, 

 greatly enlarged. (Altered 

 slightly from Carter.) The test 

 is composed of angular grains 

 of transparent quartz, within 

 which is the transparent ecto- 

 sarc, lined by the finely granu- 

 lar endosarc. n Nucleus ; c c 

 Contractile vesicles. 



