Viscosity Changes of Protoplasm 175 



posterior end increases the contractile tension and reverses the flow 

 and repeats the cycle. There is a net gain at the anterior end and 

 a net loss at the posterior end with each cycle. 



Most of the active pieces obtained by tearing are somewhat 

 larger and more complex and have one or more branching and 

 anastomosing thick-walled tubes, one or two or more posterior 

 retracting ends, one or more thick, lobulated, anterior, advancing 

 ends which project from a broad flat plasmodial sheet with thick and 

 thin areas that grade into the tubular region. The thicker areas of 

 the sheet are traversed by branching and anastomosing channels 

 which merge into the tubes posteriorly and into minute, more or less 

 temporary, terminal channels leading to each lobule and pseudopod 

 anteriorly. The same type of organization found in the small plas- 

 molets prevails also in the larger ones and undoubtedly also in the 

 relatively enormous masses of the stock cultures under approxi- 

 mately the same conditions where growth and locomotion are fairly 

 rapid. When examining an especially selected small plasmolet a 

 millimeter or so long in a preparation 2-3 hours old, it is convenient 

 to consider separately the organization or structure and the behavior 

 of the different regions, namely, the posterior end, the tube, the fan- 

 shaped transition zone, and the anterior end. 



Posterior ends differ considerably; they may be blunt or drawn 

 out into long tenuous tapering threads. The usual blunt ones have 

 a gel wall continuous with the tubular part, but it is not, as a rule, 

 quite as thick as the latter. Sometimes there is an outer hyaline zone 

 and sometimes not, depending upon the condition of the plasmodium. 

 In the course of a few minutes the hyaline zone may completely dis- 

 appear and then reappear again. Sharp hyaline spicules such as 

 Camp pictures at the posterior end may come and go in the course 

 of a few minutes. The limits of what one might designate as the 

 posterior end are rather indefinite as its gel layer merges into the 

 gel wall of the tube and they function more or less as a unit. One 

 might limit it to the region where during contraction and forward 

 flow of the endoplasm some of the gel layer solates and mixes with 

 the endoplasm. The two most interesting points about the posterior 

 end are its contraction and the partial solation of its gel layer during 

 the contraction. One can see this local contraction of the posterior 

 end and often in addition to this a more general shortening of the 

 posterior part of the tube which pulls the posterior end forward 

 rather rapidly at the time of the forward flow of the endoplasm. 

 Solation at the posterior end occurs during the contractile phase only 



