BEHAVIOR OF THE LOWER ORGANISMS 



containing no granules; this is called the ectosarc (Fig. i, ec.). Within 

 this the protoplasm is granular, and contains bits of substance taken as 

 food, vacuoles filled with water, and certain other structures. This 



granular protoplasm is known as the 

 endosarc (Fig. i, en.). Within the 

 fluidlike endosarc we find two well- 

 defined structures. One is a disk- 

 like or rounded, more solid body, 

 *dy(i8 79 ). ^0^ as the nucleus (Fig> If WM>)> 



The other is a spherical globule of water, which at intervals collapses, 



emptying the contained water to the outside. This is the contractile 



vacuole (Fig. i, c.v.). 



There are many different kinds of Amoebae, varying in their appear- 

 ance and structure. For our purposes it will be sufficient to distinguish 



three main types. In one type the form is very 



irregular and changeable, and there are many 



pseudopodia. Of this type Amoeba proteus (Fig. 



i) is the commonest species. In a second type 



the animal usually moves forward rapidly as a 



single elongated mass, the protoplasm seeming very 



fluid. Amoeba Umax (Fig. 2) is a representative 



of this group. A third type consists of slowly 



moving Amoebae, of nearly constant form, usually having wrinkles on the 



surface, and with the thick ectosarc much stiffened, so that it does not 



appear fluid in character. The commonest representative of this type 



is Amceba verrucosa (Fig. 3). 



In its usual locomotion the movement of Amoeba is in many respects 



comparable to rolling, the upper surface continually passing forward 



and rolling under at the anterior end, so as to 

 form the lower surface. This may best be 

 seen by mingling soot with water containing 

 many Amoebae. Fine granules of soot cling 

 readily to the surface of Amoebae of the verru- 

 cosa type, and more rarely to Amoebae of other 

 types. Such particles which are clinging to 

 the upper surface move steadily forward till 

 they reach the anterior edge. Here they are 

 rolled over and come in contact with the sub- 

 stratum. They then remain quiet till the 

 Amoeba has passed across them. Then they 

 pass upward again at the posterior end, and 

 forward once more to the anterior edge. This 



FIG. 3. A mctba verru- 

 cosa, after Leidy (1879). 



FIG. 4. Paths of two par- 

 ticles attached to the outer sur- 

 face of Amceba. That portion 

 of the paths that is on the lower 

 surface is represented by broken 

 lines. The two particles were 

 seen to complete the circuit of 

 the animal five or six times in 

 the paths shown. (The Amoeba 

 was of course progressing ; no 

 attempt is made to represent 

 this in the figure.) 



