162 THE BEHAVIOR OF LOWER ORGANISMS. 



the advancing edge. This condition is not at all rare. In such cases 

 there is at the anterior end less clear space between the granular region 

 and the water than in any other part of the body. In fact, there is 

 typically no space at all. I have seen large vacuoles come so close to 

 the anterior edge at such times that it was not possible to distinguish 

 between the boundary of the vacuole and the boundary of the Amoeba 

 (Fig. 52, 3). 



4. Finally, either hyaloplasm or endosarc or both may stop in any 

 of the positions mentioned above. Thus the hyaloplasm may stop, 

 whereupon the endosarc flows into it and fills it, or both may stop, so 

 that the hyaloplasm remains empty, as a clear band, for a long time. 



The line separating hyaloplasm and endosarc is at times very sharply 

 defined, as has often been pointed out. A number of unusually favorable 

 specimens gave me the opportunity of determining the reason for this, 

 in many cases at least. The Amoeba in question (Fig. 52, c-f) was an 

 elongated, rapidly moving form, much resembling A. Umax, but having 

 usually two contractile vacuoles, one very large, in the fore part of the 

 body, the other smaller and in the rear. The body contained many 

 fine granules, which, when the animal was at rest, were scattered almost 

 uniformly through the body; the peripheral, more solid zone (usually 

 called ectosarc) contained as many of these as did the endosarc. 



In moving this Amoeba usually sends out first a large amount of clear 

 fluid containing no granules ; this at times extends so far as to constitute 

 half the length of the Amoeba (Fig. 52, c}. There is a perfectly sharp 

 line between the clear hyaloplasm and the granular endosarc, and behind 

 this line the granules of the endosarc are heaped up, as if under pressure. 

 Suddenly this line gives way over a small area (at #), and the granules 

 pour through it in a thin stream nearly or quite to the anterior tip of 

 the Amoeba (Fig. 52, d}.* Gradually the whole barrier gives way, and 

 nothing is left to mark the position it occupied. If after its first out- 

 flow the hyaloplasm has stopped, the whole Amoeba is filled with 

 granules. But if, as is usually the case, after a pause the hyaloplasm 

 has started forward again, the granules of the endosarc stream forward 

 not to the anterior tip, but only to the line 'which formed the anterior 

 boitndary of the hyaloplasm at its pause (x-y, Fig. 52, e,f). Here 

 the granules stop and are heaped up again, until finally the barrier 

 breaks as before, and the granules rush forward again, to be stopped 

 at a new line. 



The explanation of these phenomena becomes evident on careful 

 examination. It is to be noted that the line x-y which stops the 

 flow of the granules of endosarc is always identical with one which 



* Similar phenomena have been observed by Prowazek (1900, p. 17 ; Fig. 18). 



