444 RHIZOPODA LOBOSAI AMCEBA. 



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. A Contractile Vesicle 

 seems also to be uniformly present; though it does not usually 

 make itself so conspicuous by its external prominence as it does in 

 A ctinophrys. 



332. In all these particulars, therefore, the Amcebina present 

 a nearer approach to Infusoria than is discernible among other 

 Rhizopods ; and 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. 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 ex- 

 terior is composed possesses considerable tenacity. No movement 

 of granules can be seen to take place along the surface of the 

 pseudopodia ; and when two of these organs come into contact, 

 they scarcely show any disposition even to mutual cohesion, still 

 less to a 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 latter is undergoing 

 rapid elongation ; whilst a like current may set towards the centre 

 of the body from some other protrusion which is being withdrawn 

 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 accom- 

 plished, 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 j but it is maintained by MM. 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 en- 

 counters 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 



