Page:Natural History Review (1861).djvu/476

464 diffused, on which the hue and opacity of the body depend; its central portion seems to have an almost aqueous consistence, the granular particles being seen to move quite freely upon one another, with every change in the shape of the body; but its peripheral portion is more viscid, and graduates insensibly into the firmer substance of the ectosarc. The ectosarc, which is perfectly pellucid, forms an almost membranous investment to the endosarc; still, it is not possessed of such tenacity as to oppose a solution of its continuity at any point, for the introduction of alimentary particles, or for the extrusion of effete matter; and thus there is no evidence, in Amœba and its immediate allies, of the existence of any more definite orifice, either oral or anal, than exists in other Rhizopods. It is asserted by MM. Claparède and Lachmann, however, that an oral orifice does exist in Podostoma, a peculiar modification of the Amœban type; and they think it not impossible that such an aperture may exist even in Amœba, of which the lips might be exactly applied to one another, as in Amphileptus, so as only to open for the ingestion of food. The more advanced differentiation of the ectosarc and the endosarc of Amœba is made evident by the effects of re-agents. If, as Auerbach has shown, an Amœba radiosa be treated with a dilute alkaline solution, the granular and molecular endosarc shrinks together and retreats towards the centre, leaving the radiating extensions of the ectosarc in the condition of cœcal tubes, of which the walls are not soluble, at the ordinary temperature, either in acetic or mineral acids, or in dilute alkaline solutions; thus agreeing with the envelope noticed by Cohn as possessed by Paramecium and other ciliated Infusoria, and with the containing membrane of ordinary animal cells. A nucleus is always distinctly visible in Amœba, adherent to the inner portion of the ectosarc, and projecting from this into the cavity occupied by the endosarc; when most perfectly seen, it presents the aspect of a clear flattened vesicle surrounding a solid and usually spherical nucleolus; it is readily soluble in alkalies and first expands and then dissolves, when treated with acetic or sulphuric acid of moderate strength; but when treated with diluted acids it is rendered darker and more distinct, in consequence of the precipitation of a finely granular substance in the clear vesicular space that surrounds the nucleolus.

In all these particulars, therefore, the Amœbina present a nearer approach to than is discernible among other Rhizopods; and hence it was not without good reason that Prof. Müller designated them "Infusorial Rhizopods." They tend towards Infusoria, also, in their higher locomotive powers, obtaining their food by actively going in search for it, instead of entrapping it and drawing it into the substance of their bodies by the agency of their extended pseudopodia. In fact, the pseudopodia are here very different organs from those of either or, being rather lobate extensions of the body itself, than appendages proceeding from its surface-layers. They are few in number, short, broad, and rounded;