442 EHIZOPODA EADIOLARIA: ACTINOPHRYS. 



may be thus occupied at one time by alimentary particles ; fre- 

 quently four to eight are thus distinguishable, and occasionally ten 

 or twelve ; Ehrenberg, in one instance, counted as many as sixteen, 

 which he described as multiple stomachs. Whilst the digestive 

 process, which usually occupies some hours, is going on, a kind of 

 slow circulation takes place in the entire mass of the Endosarc 

 with its included vacuoles. If, as often happens, the body taken 

 in as food possesses some hard indigestible portion (as the shell of 

 an Entomostracan or Rotifer), this, after the digestion of the soft 

 parts, is gradually pushed towards the surface, and is thence ex- 

 truded by a process exactly the converse of that by which it was 

 drawn in : if the particle be large, it usually escapes at once by 

 an opening which (like the mouth) extemporizes itself for the 

 occasion (Fig. 233, d); but if small, it sometimes glides along a 

 pseudopodium from its base to its point, and escapes from its 

 extremity. What is known regarding the Reproduction of Aclino- 

 phri/s will be presently stated (§ 334).* 



330. The Order Radiolaria includes various forms of Rhizopods 

 which agree with Actinophrys in the leading peculiarities of its 

 structure, but which differ in having the body included in an 

 envelope of more or less firm consistence. This may be formed 

 simply of a membranous or a chitinous exudation, as in certain 

 genera which represent in this Order the Gromia among the 

 Reticularia, and the Arcella and Difflugia among the Lobosa. 

 But the types in this group that are of most general interest to 

 the Microscopist are the Polycystina, whose bodies are furnished 

 with siliceous skeletons of most wonderful beauty and variety of 

 form and structure ; these may be more conveniently described, 

 with the Foraminifera, in a separate Chapter (Chap. x.).t 



331. Lobosa. — No example of the Rhizopod type is more common 

 in streams and ponds, Vegetable infusions, &c, than the Amoeba 

 (Fig. 234) ; a creature which cannot be described by its form, for this 

 is as changeable as that of the fabled Proteus, but which may yet be 

 definitely characterized by peculiarities that separate it from the 

 two groups already described. The distinction between Ectosarc 

 and Endosarc is here clearly marked, so that the body approaches 

 much more closely in its characters to an ordinary Cell composed 

 of cell-wall and cell-contents. It is through the Endosarc alone 

 that those coloui*ed and granular particles are diffused, on which 

 the hue and opacity of the body depend ; its central portion seems 



* The following recent Memoirs should be consulted by such as wish 

 to apply themselves to the study of this interesting organism : — Kolliker 

 and Cohn, in " Siebold and Kolliker's Zeitschrift," 1849 and 1851 ; 

 Claparede, in "Ann. of Nat. Hist.," 2nd Ser., Vol. xv., pp. 211, 285, and 

 in his " Etudes sur les Infusoires " (1865), 2ieme Partie ; Weston, in 

 " Quart. Journ. of Microsc. Science," Vol. iv., p. 116. 



t It is maintained by Dr. Wallich (loc. cit.) that the Polycystina should 

 be placed in the same Order with the Foraminifera ; the characters of 

 the Sarcode-body being essentially the same in both groups. 



