140 THE BEHAVIOR OF LOWER ORGANISMS. 



AMCEBA VKRRUCOSA AND ITS RELATIVES. 



In giving an account of the experiments which demonstrate this, I 

 shall begin with species of Amoeba in which pseudopodia are, as a rule, 

 not formed, and the movements are uniform in character, since here the 

 conditions are simplest from our present standpoint. For this purpose 

 Amoeba verrucosa Ehr., and particularly the transparent form known 

 as A. sphceronucleolus Greef, are favorable. In these Amoebae particles 

 cling rather easily to the outer surface. 



When a quantity of soot is added to the water containing Amoebae 

 of the species named, small masses cling to the surface of the animal. 

 Such a mass, attached to the upper surface, shows the following 

 movements : It passes slowly forward (Fig. 38) , then over the anterior 

 edge, and under the latter. Here it stops, while the Amoeba continues 

 to move forward. The mass of soot remains quiet until the entire 

 Amoeba has passed over it and it lies beneath the posterior end. It 

 now passes upward again, to the upper surface (Figs. 39, 40), then 

 forward once more to the anterior end. Here it goes under the Amoeba 



as before, to be carried upward and forward again when the posterior 

 end passes over it. 



These observations are made with absolute ease, and there is no pos- 

 sibility of mistaking internal particles for external ones. Particles lying 

 in the water outside the Amoeba may be seen to become attached at the 

 posterior end, to pass upward, lying distinctly outside the boundary of 

 the protoplasm (Fig. 38, posterior end), then forward, till as they double 

 the anterior end they are again seen sharply defined outside the boundary 



* FIG. 40. Diagram of the movements of a particle attached to the surface of 

 Amoeba verrucosa, in side view. In position i the particle is at the posterior 

 end ; as the Amoeba progresses it moves forward, as shown at 2, and when the 

 Amoeba has reached the position 3 the particle is at its anterior edge, at x. 

 Here it is rolled under and remains in position, so that when the Amoeba has 

 reached the position 4 the particle is still at x, at the middle of its lower surface. 

 In the position 5 the particle is still in the same place, x, save that it is lifted 

 upward a little as the posterior end of the Amoeba becomes free from the sub- 

 stratum. Now as the Amoeba passes forward the particle is carried to the upper 

 surface, as shown at 6. (Thence it continues forward and again passes beneath 

 the Amoeba, etc.) The broken lines show that part of the surface of the Amoeba 

 which is at rest. 



