4 AMCEBA 



these two constituents will always be found to have the 

 same relations, whence we conclude that an Amoeba con- 

 sists of a granular substance the endosarc, completely 

 surrounded by a clear transparent layer or ectosarc. 



One very noticeable thing about Amoeba is that it is never 

 quite the same shape for long together. Often the changes 

 of form are so slow as to be almost imperceptible, like the 

 movements of the hour-hand of a watch, but by examining 

 it at successive intervals the alteration becomes perfectly 

 obvious, and at the end of half an hour it will probably 

 have altered so much as to be hardly like the same thing. 



In an active specimen the way in which the changes of 

 form are brought about is easily seen. At a particular 

 point the ectosarc is pushed out in the form of a small 

 pimple-like elevation (Fig. i. A, left side) : this increases in 

 size, still consisting of ectosarc only, until at last granules 

 from the endosarc stream into it, and the projection or 

 pseudopod (A, c, E, psd) comes to have the same structure 

 as the rest of the Amoeba. It must not be forgotten that as 

 the animal does not alter perceptibly in volume during the 

 process, every pseudopod thus protruded from one part of 

 the body necessitates the withdrawal of an equal volume 

 from some other part. 



This peculiar mode of movement may be illustrated by 

 taking an irregular lump of clay or putty and squeezing it 

 between the ringers. As it is compressed in one direction 

 it will elongate in another, and the squeezing process may 

 be regulated so as to cause the protrusion of comparatively 

 narrow portions from the solid lump, when the resemblance 

 to the movements described in the preceding paragraph will 

 be fairly close. Only it must be borne in mind that in 

 Amoeba there is no external compression, the " squeezing " 

 being done by the animalcule itself. 



