436 GENERAL CHARACTERS OF RHIZOPODS. 



out into the substance of the body at any point. That body may 

 be almost entirely enclosed within a shelly or horny casing ; but 

 one or more apertures always exist in that casing, through which 

 the prolongations of the sarcode-body are put forth ; and the 

 particles of food introduced by their instrumentality no more enter 

 into the interior of that body by any definite mouth, than they do 

 in the naked or shell -less forms. In the lowest Rhizopods, indeed, 

 there seems no distinction whatever between the containing and 

 the contained portion of the sarcode-body, the whole being ap- 

 parently composed of a viscid homogeneous protoplasm. In the 

 highest, which most nearly approach those more elevated Protozoa 

 that exhibit a more or less definite organization, there is a decided 

 differentiation between the external or containing and the internal 

 or contained portion of the sarcode-body ; to the former, which 

 sometimes has an almost membranous firmness, the name Ecto- 

 sarc has been given ; whilst the latter, which is a liquid of almost 

 watery thinness, has received the name of Enclosure. Now upon 

 the degree of this differentiation between the Ectosarc and the 

 Endosarc depends the character of the Pseudopodial prolonga- 

 tions ; and these may present themselves under three distinct 

 conditions ; namely (1), as indefinite extensions of the viscid 

 homogeneous Protoplasm, freely branching and subdividing into 

 threads of extreme tenuity, and undergoing complete mutual 

 coalescence wherever they come into contact (Fig. 232), so as 

 to form an irregular network that may be likened to an animated 

 Spider's- web ; (2) as more definite rod-like extensions of the 

 Ectosarc, having a more or less regular radiating arrangement 

 (Fig. 233), and exhibiting little disposition either to ramify or to 

 coalesce, so as almost constantly to maintain their distinctness ; 

 (3) as lobose extensions of the body itself, having like it an 

 almost membranous Ectosarc with a very liquid Endosarc, and 

 exhibiting an entire absence of any tendency either to ramify or 

 to coalesce when they come into mutual contact (Figs. 234, 235). 

 To the first of the Orders thus marked-out, the name Reticularia 

 seems appropriate ; the second have been distinguished as Radio- 

 laria ; and the third may be designated Lobosa. It must be freely 

 admitted, however, that these groups cannot be distinctly marked 

 out ; the typical examples which will now be described being con- 

 nected by many intermediate forms. This is not to be wondered 

 at, when the extreme indefiniteness which characterizes this lowest 

 type of Animal existence is duly borne in mind.* 



* For a more detailed exposition of his " Systematic Arrangement of 

 the Rhizopoda," see the Author's Memoir on that subject in the "Natural 

 History Review," October, 18C1 ; and his " Introduction to the Study of 

 the Foraminifera," published by the Ray Society, 1862. — Another Classifi- 

 cation has been more recently proposed by Dr. Wallich, whose Memoir on 

 the Structure and Affinities of the Polycystina ("Transact, of Microsc. 

 Society," N.S., Vol. xiii., 1865, p. 57) contains much important information 



