24 OF THE RHIZOPODA IN GENERAL:— LOBOSA. 



inclosed in a proper membranous envelope ; for this investment seems ready to yield at any 

 point, so as to give exit to the pseudopodial projections put forth by the softer contractile 

 ectosarc (fig. 17, b). And in ordinary Amoebce, which have no double contour line (figs. 15, 

 16), it seems most likely that alimentary and other substances can be introduced through 

 any part of the ectosarc into the interior, as in AdinopJtrt/s, and that indigestible bodies 

 can be extruded in like manner, though previously to their escape they may often be seen 

 to push the ectosarc before them, so as to form considerable projections from the surface of 

 the body. The central portion of the endosarc seems to have an almost aqueous consistence, 

 the granular particles diffused through it (which are, for the most part, derived directly from 

 without) being seen to move very freely upon one another with every change in the shape of 

 the body. There is not, however, a definite limitation between the wall and the contents of 

 this cavity ; for the peripheral portion of the endosarc is much more tenacious than the 

 central, and seems to graduate insensibly into the firmer substance of the ectosarc. In the 

 typical forms of Amoeba (as A. prhiceps, fig. 16, and A. radiosa, fig. 15), the endosarc 

 passes into the interior of the pseudopodial extensions. But in A. bilimbosa (fig. 17) and 

 some otiier forms, in which the differentiation of the endosarc and the ectosarc is unusually 

 great, these extensions are derived from the latter only. In A. porrecta (fig. 18), on the other 

 hand, the differentiation is far less complete, and the pseudopodia seem to be as much 

 formed by tlie endosarc as by the ectosarc; in this and other particulars presenting a link of 

 transition to the shell-less Reticulosa. 



23. A "nucleus" [n, figs. 15, c, 17, a) is always distinctly visible in Amoeba, having, 

 when most perfectly seen, the aspect of a clear, flattened vesicle surrounding a solid and 

 usually spherical nucleolus; it is adherent to the inner portion of the ectosarc, and projects 

 from it into the general cavity. — A " contractile vesicle " seems also to be uniformly present ; 

 though it does not usually make itself so obvious by its external prominence as it 

 does in Aclinopltri/s. 



24. The more advanced differentiation of the central and peripheral portions of the pro- 

 toplasmic body of Amoeba is made evident by the effects of reagents. If an A. radiosa 

 (fig. 15) 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 cscal 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 membrane of ordinary animal cells. The nucleus and nucleolus are 

 readily soluble in alkalies, whilst they are rendered darker and more distinct by dilute acetic 

 or sulphuric acid, in consequence of the precipitation of a finely granular substance in the 

 clear vesicular space that surrounds the nucleolus. When treated with more concentrated 

 acids, the nucleus and nucleolus first expand and then dissolve. 



25. The Amoeba and its allies are distinguished in a very marked manner from all other 

 Rhizopods by the comparative activity of their locomotion ; instead of remaining fixed to one 

 spot (except when made to change their place by external agency), and entrapping their food 



