136 THE BEHAVIOR OF LOWER ORGANISMS. 



indefinitely. In favorable cases I have repeatedly followed a single 

 granule from the posterior end forward till it came to rest at the 

 anterior end, then watched the body of the Amoeba pass it by, until it 

 was again at the posterior end and started forward anew. The course 

 of a single granule is represented in Fig. 36. As is evident from this 

 figure, the granule does not travel backward in any part of its course. 

 Not all the granules, however, remain quiet until they have passed to 

 the posterior end. Many of them are taken again into the central 

 stream before the entire body of the Amoeba has passed them. Large 

 granules usually stop only a short time, starting forward again before 

 the middle of the Amoeba has reached them ; others are taken up at the 

 middle or farther back, while many smaller granules reach the posterior 

 end. But as a rule none show any movement backward, so far as I 

 have observed. 



It is not only at the margins of the Amoeba, but also on the under 

 surface, in contact with the substratum, that the ectosarc with its 

 granules is at rest or moving slowly forward in the posterior half. 

 This is evident when the lower surface of a transparent Amoeba is 

 brought into focus. 



2 That excellent observer, 



Dr. Wallich, saw clearly 

 many years ago that there 

 is really no backward cur- 



Q> j 'c d e J rent, though at first view 



FIG. 36.* there appears to be such. 



It is only necessary to watch a specimen of Amoeba carefully to become con- 

 vinced that the appearance of a returning, as well as an advancing, stream of 

 granules is illusory. The stream, it will be observed, is invariably in the direc- 

 tion of the preponderating pseudopodial projections. The particles simply flow 

 along with the advancing rush of protoplasm. There is no return stream, but 

 the semblance of one is engendered by one layer of particles remaining at rest 

 whilst another is moving past them. (Wallich, 1863, , p. 331.) 



This statement of the facts my observations fully confirm. 

 In this account of the lack of backward movement in the granules 

 of the ectosarc on the lower surface and at the margins I find myself 



*FiG. 36. Diagram of the movements of a single particle in Amoeba, as 

 seen from above. The particle begins at a, passes to b and then to c, at the 

 anterior edge of the Amoeba shown in the outline i. The Amoeba now passes 

 forward to the position 2. and thence to 3, while the particle retains the posi- 

 tion c; when the Amoeba has reached the position 3 the particle is thus at 

 its posterior end. Now the particle moves forward again, from c to </, and 

 thence to e and/", thus coming again to the anterior edge. Here it stops, as at 

 c, until the body of the Amoeba has passed it. As the figure shows, the particle 

 does not move backward in any part of its course. 



