16 THE MICROSCOPE AND ITS REVELATIONS. 



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 ordi- 

 nary animal cells. A 'nucleus/ N, is always distinctly visible in Amoeba, 

 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 ex- 

 pands and then dissolves when treated with acetic or sulphuric acid of 

 moderate strength; but when treated with dilute acid 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 nucle- 

 olus. A ' contractile vesicle,' cv, seems also to be uniformly present, 

 though it does not usually make itself so conspicuous by its external 

 prominence as it does in Actinoplirys ; and the neighboring part of the 

 body is often prolonged into a set of villous processes VIL, the presence 

 of which has been thought by some to mark a specific distinction, but 

 which seems too variable and transitory to be so regarded. 



404. The pseudopodia, which are not so much appendages, as lobate 

 extensions of the body itself, are few in number, short, broad, and 

 rounded; and their outlines present a sharpness which indicates that the 

 substance of which their exterior is composed possesses considerable tena- 

 city. No movement of granules can be seen to take place along the sur- 

 face of the pseudopodia: and when two of these organs come into contact, 

 they scarcely show any disposition even to mutual cohesion, still less to 

 fusion of their substance. Sometimes the protrusion seems to be formed 

 by the ectosarc alone, but more commonly the endosarc also extends into 

 it, and an active current of granules may be seen to pass from what was 

 previously the centre of the body into the protruded portion, when the lat- 

 ter is undergoing rapid elongation; whilst a light current may set towards 

 the centre of the body from some other protrusion which is being with- 

 drawn into it. It is in this manner that an Amoeba moves from place to 

 place; a protrusion like the finger of a glove being first formed, into 

 which the substance of the body itself is gradually transferred; and 

 another protrusion being put forth, either in the same or in some different 

 direction, so soon as this transference has been accomplished, or even 

 before it is complete. The kind of progression thus executed by an 

 Amoeba is described by most observers as a ' rolling ' movement, this being 

 certainly the aspect which it commonly seems to present; but it is main- 

 tained by M.M. Claparede and Lachmann that the appearance of rolling 

 is an optical illusion, for that the nucleus and contractile vesicle always- 

 maintain the same position relatively to the rest of the body, and that 

 ' creeping* would be a truer description of their mode of progression. It 

 is in the course of this movement from place to place, that the Amoeba 

 encounters particles which are fitted to afford it nourishment: and it 

 appears to receive such particles into its interior through any part of the 

 ectosarc, whether of the body itself or of any of its lobose expansions; in- 

 soluble particles which resist the digestive process being got rid of in the 

 like primitive fashion. 



405. It may often be seen that portions of the sarcode-body of an 

 Amceba, detached from the rest, can maintain an independent existence;, 

 and it is probable that such separation of fragments is an ordinary mode 

 of increase in this group. When a pseudopodial lobe has been put-forth 

 to a considerable length, and has become enlarged and fixed at its extrem- 



