Literary Notices. 171 



that the movements of Amceba are due to changes in surface tension. 

 Jennings, on the basis of careful observation of the movements of 

 several species of iVmoeba, states that there are no side or backward 

 currents, but that the process occurs as follows : "In an advancing 

 Amceba substance flows forward on the upper surface, rolls over at 

 the anterior edge, coming in contact with the substratum, then remains 

 quiet until the body of the Amoeba has passed over it. It then moves 

 upward at the posterior end, and forward again on the upper surface, 

 continuing in rotation as long as the Amoeba continues to progress. 

 The motion of the upper surface is congruent with that of the endo- 

 sarc, the two forming a single stream " p. 148. 



Accurate and detailed descriptions are given of the processes of 

 formation and withdrawal of pseudopodia, and it is shown that con- 

 tractility is a capacity of the ectosarc. "Altogether, then, our results 

 lead us to look upon Amceba as an elastic and contractile sac, con- 

 taining fluid. In locomotion one side actively stretches out, becomes 

 attached to the substratum, and draws the remainder of the sac after 

 it in a rolling movement. The primary phenomena are the stretching 

 out of one side, the elasticity, and the contractility of the outer layer" 

 p. 172. 



Under the subject of reactions, the author presents the results of 

 extensive studies of the influence of different stimuli upon Amoeba. 

 He distinguishes three classes of reaction : the positive, the negative, 

 and a complex feeding reaction. Several interesting instances of the 

 pursuit of food are cited in support of the author's opinion that the 

 behavior is by no means so simple and uniform as is commonly sup- 

 posed. 



After redescribing the protoplasmic movements of Amoeba in the 

 light of his own observations, the author discusses the physics of loco- 

 motion with results which may most fitly be expressed in his own 

 words. "Putting all our results together we must conclude that the 

 movements and reactions of Amoeba have as yet by no means been 

 resolved into their physical components. Amoeba is a drop of fluid 

 which moves in its usual locomotion in much the same way as inor- 

 ganic drops move under the influence of similarly directed forces. 

 But what these forces are is by no means clear. When we take into 

 consideration the currents as they actually exist, local decrease in sur- 

 face tension breaks down completely as an explanation for the locomo- 

 tion and other movements. The locomotion taken by itself might be 

 explained as due to the adhesion of the fluid protoplasm to solids. 



