THE SIMPLER ORGANISMS 



71 



Different individuals will differ much in clearness of these 

 parts, according as they have recently eaten much or little. 

 The very clear external protoplasmic layer is generally 

 known as ectosarc. It shows no definite cell wall, but 

 only an enveloping film ; hardly more of this than may be 

 accounted for by surface tension of the body fluids. It 

 has in amoeba developed no external skeleton, but remains 

 so clear that we may here observe nearly simple naked 

 protoplasm, unobscured by anything, and in action. The 

 movements seen here are quite different from the simple 

 streaming motion in a single current of the intemodal cell 

 of Nitella; they are of a higher order of complexity. A 

 portion of the body substance may be pushed out in any 

 direction, but always in the direction of locomotion, forming 



Fig. 52. Amoeba. Diagram illustrating in /, 2, 3, food intake; 

 in 4, 3, 6, removal of indigestible residue; s, a food organism; 

 p, the same occupying a food vacuole, recentlv engulfed; g, the 

 same partly digested; r, residue of same, discharged. 



the broadly rounded lobes called pseudopodia: first the 

 ectosarc pushes out, and then the granular endosarc streams 

 forward into it. Pushing out forward, and pulling up from 

 the rear is the process of locomotion, and it is dependent 

 solely upon the contractility of protoplasm. 



By this same power feeding is accomplished. Two 

 pseudopodia (fig. 52 J-j) encircle a suitable bit of food, and 

 press it into the interior of the body, where, engulfed by the 

 protoplasm, it is digested : any indigestible residue is gotten 

 rid of by the reverse process — the protoplasm flows away 

 from it and leaves it behind (fig. 52 4-6). 



These activities imply volition of some sort or degree, 

 for there appears to be some selection of food and some 

 spontaneity of movement: changes of direction, the taking 



