148 THE BEHAVIOR OF LOWER ORGANISMS. 



are important. Particles situated on the upper surface move usually 

 at the same, or nearly the same, rate as the granules beneath them, in 

 the endosarc. The movement of the surface particles follows exactly 

 that of the endosarc beneath them, changing in direction when the latter 

 changes. Two particles close together on the upper surface may thus 

 diverge or even flow in opposite directions, carried by two different 

 currents which are visible in the endosarc. Any portion of the ecto- 

 sarc, like any portion of the interior, may stop at any time, while other 

 parts flow onward. One may thus see at times a particle at rest on the 

 upper surface of a moving Amoeba. Isolated observations of this kind 

 might lead one to suppose that the upper surface, like the lower, remains 

 at rest while the endosarc passes forward. But when a particle on the 

 surface is at rest, one will usually find, by a proper change of focus, 

 that the endosarc beneath it is likewise at rest. It is, of course, well 

 known that certain portions of the endosarc may be at rest while the 

 remainder is in movement (see Rhumbler, 1898, p. 122). In the same 

 way a portion of the outer layer may sometimes be at rest while the 

 adjacent endosarc is in motion ; this, however, is rather unusual. 



We may sum up our results thus far in the following statements : 

 In an advancing Amoeba substance flows forward on the upper sur- 

 face, 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 endosarc, the two forming a 

 single stream. 



HISTORICAL, ON ROLLING MOVEMENTS IN AMOEBA. 



The possibility that Amoeba progresses by a rolling movement was 

 discussed by Claparede & Lachmann (1858). In Amoeba Umax and 

 A?nceba quadrilineata (= A. verrucosd), according to these authors, 

 the general appearance of locomotion is in many respects in favor of 

 this view : " On croit positivement voir 1'animal rouler sur lui-meme " 

 (p. 435). But this correct view is rejected (in the text) because of the 

 (supposed) permanence in the position of the contractile vacuole. 

 Claparede & Lachmann insist that the contractile vacuole is situated 

 in the ectosarc ; hence, they argue, if there were a rolling movement 

 of the ectosarc. the vacuole would necessarily partake of the movement ! 

 In a note on p. 437 it is stated, however, that Lachmann personally 

 believed the motion to be of this rolling character. " II croit s'etre 

 assure" que r A. quadrilineata roule sur elle-meme." According to 

 Claparede & Lachmann, Perty held this view also. 



