CABPEXTEB ON THE A U i; vm ! ;:\; I \ I or THE BHIZOPODi. 165 



and their oulliiuvs present n sharpness Which indicates tluit the sub- 

 stance of which their exterior is composed possebooi considerable 



tenacity. No movement of granules can be scon to take place along 



the surface of the pseudopodia ; and when two of these organs come 

 into contact, they scarcely show any disposition c\en to mntnal 

 cohesion, still less to a J'usion of their substance. .Sometimes the 

 protrusion seems to be formed by the ectosaiv alone, but more com- 

 monly the endosarc also passes into it, and an active; current of 

 granules maybe seen to pass from what was prc\iuiislv the centre 

 of the body, into the protruded portion, when the latter id" 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 of the body from some other protrusion which is being withdrawn 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 placet;) 

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

 which the substance of the body itself is gradually transferred j 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" move- 

 ment, this being certainly the aspect which it commonly seems to 

 present ; 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," or reptation, 

 would be a truer description of their mode of movement. On this 

 view, these animals have their ventral constantly differential ed from 

 their dorsal surface, it being from the former alone that the pseudo- 

 podian extensions proceed ; and thus a transition would seem to be 

 indicated towards the testaceous Amcebina {Arcclla, Diffluyia, <fcc.) 

 in which the dorsal surface is invested by a shell, and the pseudopodia 

 are strictly limited to the ventral region. It is in the course of its 

 movement from place to place, that the Amoeba encounters particle* 

 which are fitted to ailbrd 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. 



The Amoeban, like the Actinophryan, type shows itself in the 

 testaceous as well as in the naked form ; and it is of importance to 

 notice, that whilst the "test" of Arcella^ix formed by a lnemhranous 

 (probably chitinous) exudation from the animal itself, that of JDif- 

 flugia is chiefly made up of grains of sand, fragments of shell, or oilu r 

 foreign particles, cemented together. Hie resemblance of tin 1 animals 

 of these two genera is so close, that DO systcmalist has ever proposed 

 to separate them by more than a generic distinction ; and if ilie dis- 

 similarity of the material of llieir "test'' be not admitted as a 

 differential character of grave importancej I can see no reason f r 

 attaching more weight to the distinc ion between the chitinous 

 of Gromia and the calcareous shell of the ordinary Foramini 



