142 THE BEHAVIOR OF LOWER ORGANISMS. 



the opposite direction, so that the former posterior end became anterior. 

 At the same time the two particles reversed their former motion and 

 began to travel back in the direction from which they had come that 

 is, toward the new anterior end. They were observed to make several 

 complete turns about the Amoeba while moving in this new direction. 

 I will not, however, add further details, as those above recounted are 

 sufficient to give a conception of the main features of the movement. 



Thus two definite points on the surface of an Amoeba may retain 

 nearly the same relation to one another for five or six complete revolu- 

 tions, though their distance apart and their relative position may vary 

 a little. The reversal of the direction of rotation when the direction of 

 locomotion is reversed, described in the above case, I have seen many 

 times. 



The direction of the movement of particles on the outer surface is 

 the same as that of the underlying particles of endosarc. The rate is 

 also about the same as for the endosarc, though often, or perhaps 

 usually, the outer particles move a little more slowly than those in the 

 endosarc. 



It is not merely a thin outer layer that has the rolling movement. 

 This is demonstrated by the movements of bodies that are partly 

 embedded in the substance of the Amoeba. For example, a large 

 Euglena cyst had become attached to the hinder end of an Amoeba 

 sphceronucleolus. The cyst was carried upward and forward on the 

 upper surface, and at the same time it began to sink into the protoplasm, 

 so that when it had reached the anterior edge it was partially embedded. 

 It was then rolled under, remained at rest on the under surface in the 

 usual way, and came up at the posterior end. It was now deeply sunk 

 in the protoplasm, yet it moved forward in the usual way. By the 

 time it had reached the anterior edge again it no longer protruded 

 above the surface at all. After turning the anterior edge again it sank 

 completely into the body, still surrounded by a layer of ectosarc, so 

 that it passed to the interior of the Amoeba as a food body. I have 

 repeatedly seen bodies which were thus carried forward on the upper 

 surface gradually taken in as food. They always continue the forward 

 movement even when completely embedded in the ectosarc. It is thus 

 evident that the whole thickness of the ectosarc partakes of the forward 

 movement. The forward stream in ectosarc and endosarc are one and 

 continuous. 



The relation of the movements of the outer layer to the lines and 

 wrinkles seen on the upper surface of Amoeba verrucosa and its rela- 

 tives is of interest. There are usually two sets of these wrinkles, one 

 set diverging from the posterior end toward the direction in which the 

 animal is moving, the other set forming a number of curved lines 



