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SCIENCE. 



[N. S. Vol. XX. No. 518. 



toward the oral region by the ciliary move- 

 ments. The same conditions obtain in the 

 Eotifera, for there, the ciliary current passes 

 to the mouth, on the ventral side, and the 

 organism, in case the current carries a stimu- 

 lating substance, turns toward the dorsal sur- 

 face. 



Turning our attention now to the second 

 subject-group, we find that Jennings undertook 

 the study of the behavior of Amoeba with two 

 definite purposes in mind: (1) To determine 

 how far recent physical theories explain the 

 activities of the organism, and (2) to add to, 

 systematize and unify our knowledge of the 

 subject. 



Fortunately the author did not confine him- 

 self to the unexplored regions of his field of 

 research, but instead repeated the experiments 

 and attempted to verify or replace the so-called 

 facts of other investigators, and test their 

 theories. 



The results of this thorough reinvestigation 

 of the subject are in many respects startling. 

 In the first place, Jennings finds that the de- 

 scriptions of the protoplasmic currents within 

 the moving Amceba given by Biitschli and 

 Ehumbler are not true to the facts. These 

 investigators have stated that there is a for- 

 ward-moving axial current and a backward- 

 moving surface current at the sides of the ani- 

 mal, the conditions in the organism being 

 practically the same as that in a drop of inor- 

 ganic substance whose surface tension is de- 

 creased at some point. Jennings has been able 

 to demonstrate to his entire satisfaction by 

 the use of several simple methods that there 

 is only a forward current. As this is an im- 

 portant matter we may appeal to his excel- 

 lent description of the observations. " In an 

 advancing Amcsba 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 rota- 

 tion as long as the Amoeba continues to pro- 

 gress. The motion of the upper surface is 

 congruent with that of the endosare, the two 

 forming a single stream" (p. 148). 



This is of special interest because it sweeps 

 away one of the principal supports of the sur- 

 face-tension explanation of the movements of 

 Amoeba. And it may well be added here that 

 Jennings's methods are so much superior to 

 those employed by many of the earlier investi- 

 gators, and his observations so much more de- 

 tailed, that his results will almost undoubtedly 

 be verified by others shortly. 



After a minute study of the formation of 

 pseudopodia, the reactions to stimuli, food- 

 taking, and several other interesting features 

 of the behavior of the organism, the author 

 formulates the following general conclusions 

 with respect to the mechanism of movement: 

 " Altogether, then, our results lead us to look 

 upon Amosba as an elastic and contractile 

 sac, containing fluid. In locomotion one side 

 of this sac actively stretches out, becomes 

 attached to the substratum, and draws the re- 

 mainder of the sac after it in a rolling move- 

 ment. The primary phenomena are the 

 stretching of one side, the elasticity, and the 

 contractility of the outer layer" (p. 1Y2). 

 The author does not attempt to account for 

 the pushing out of the anterior edge, nor does 

 he theorize concerning the nature of the con- 

 tractility of the ectosarc. 



Perhaps the most important general results 

 of the study, so far as the views of the author 

 are concerned, is that it shows pretty conclu- 

 sively that we have not thus far succeeded in 

 analyzing, as Biitschli, Ehumbler and others 

 appear to think they have done, the behavior 

 of any organism to the point of complete phys- 

 ical explanation. After all the external fac- 

 tors have been taken into account there ap- 

 pears still to be a necessary factor or complex 

 of factors which have to be referred to the or- 

 ganism itself. External physical factors ap- 

 parently suffice for the description of certain of 

 the activities of the lower organisms as well as 

 of the higher; but usually critical research 

 shows that the descriptions are not complete. 

 As Jennings remarks, ' Putting all our results 

 together, we must conclude that the movements 

 and reaction of Amoeba have as yet by no 

 means been resolved into their physical com- 

 ponents ' (p. 225). 



In the third group of papers the author 



