1 84 



THE BEHAVIOR OF LOWER ORGANISMS 



wrinkled or bore a pronounced roughened "tail," it is to be noticed 

 that the new pseudopodium does not flow out directly from this, but to 

 one side of it or above it (Fig. 67). Then as the Amoeba moves in the 

 reverse direction the body passes the old " tail," which finally brings 

 up the rear again, fusing with the rough area produced by contraction of 

 the region stimulated (Fig. 67, b). Of course, the new pseudopodium 

 formed must come in contact with the substratum and become attached 

 to it before locomotion in the new direction can occur. Sometimes 

 the new pseudopodium formed is sent directly upward into the water ; 

 then there is no locomotion until the Amreba topples over, bringing 

 the new pseudopodium in contact with the substratum. 



At times when the anterior end is stimulated, two new pseudopodia 

 are sent out in opposite directions on each side of the region stimulated. 



FIG. 66.* 



FIG. 67. f 



Both evidently pull on the Amosba, which becomes drawn out to form 

 a narrow isthmus between them. Finally one end pulls the other away 

 from its attachment to the bottom ; the latter then contracts, and loco- 

 motion continues in the direction of the prevailing pseudopodium. 

 There is at times a peculiar additional feature of the reaction to 



* FIG. 66. Negative reaction to a mechanical stimulus in Amoeba. An Amoeba 

 advancing in the direction shown by the arrows is stimulated strongly with the 

 glass rod at the anterior end (at a). Thereupon the currents are changed and a 

 new pseudopodium sent out as at b. 



fFic. 67. Negative reaction to a mechanical stimulus when the anterior end 

 is strongly stimulated. The arrow, *, shows the original direction of motion ; 

 the arrows in a show the currents immediately after the stimulation. A large 

 pseudopodium is sent out from above and to one side of the former tail (/), as is 

 shown by the broken outline. In b this pseudopodium has come in contact with 

 the bottom ; the arrows show the direction of the currents and of locomotion at 

 this time; /, the original tail; /', the new tail formed by the contraction of the 

 anterior end. 



