8 



BEHAVIOR OF THE LOWER ORGANISMS 



times Amoeba, on coming in contact with a solid body, turns and moves 

 toward it, — responding thus by a positive reaction. At times an 

 Amoeba which is moving along on the glass slip used in microscopic 

 work comes in contact by its upper surface with the under surface of 

 the cover-glass. Thereupon it sometimes pushes forth a pseudopodium 



Fig. 12. — Amceba velata passing from the slide to the cover-glass, side view. After Penard 

 (1002). At a the animal is creeping in the usual way, with the tentaclelike pseudopodium 

 projecting into the water. At b the pseudopodium has reached the cover-glass and attached 

 itself. At c the animal has released its hold on the slide, and is now attached to the cover alone. 



on this under surface; the pseudopodium attaches itself; the Amoeba 

 releases its hold on the slide, and now continues its course on the under 

 side of the cover-glass. Penard (1902) has observed this in Amceba 

 velata, when the long, tentaclelike anterior pseudopodium of this ani- 

 mal comes during its feeling movement in contact with the cover-glass. 

 The process is represented in Fig. 12. In a similar manner Amoebae 

 frequently pass to the under side of the surface film of water, creeping 

 on this as if it were a solid body. 



Under certain circumstances Amceba seems especially disposed 

 toward this positive reaction. Sometimes an Amoeba is left suspended 



in the water, not in contact with 

 anything solid. Under such cir- 

 cumstances the animal is as nearly 

 completely unstimulated as it is 

 possible for an Amoeba to be ; it 

 is contact only with the water, 

 and that uniformly on all sides.- 

 But such a condition is most un- 

 favorable for its normal activities ; 

 it cannot move from place to 

 place, and has no opportunity to 

 obtain food. Amoeba has a 

 method of behavior by which it 

 meets these unfavorable condi- 

 tions. It usually sends out long, 

 slender pseudopodia in all direc- 

 tions, as illustrated in Fig. 13. 

 The body may become reduced to little more than a meeting point for 



It is evident that the sending out of these long arms 



Fig. 13. — Amoeba proteus suspended in the 

 water, showing the long pseudopodia extended 

 in all directions. After Leidy (1879). 



these pseudopodia. 



