174 The Structure of Protoplasm 



The endoplasm evidently gels as the pieces are divided because 

 it does not flow out at the cut end. In the course of a few minutes 

 or so, small pseudopodia begin to extend out from the periphery 

 and show typical elongation and retraction with each outward and 

 inward flow of tiny streams of endoplasm. The pseudopodia seem to 

 be confined to the peripheral border of the piece that is in contact 

 with or close to the cover glass. The entire periphery of good, active 

 pieces, which are the ones we are considering here, may show such 

 pseudopodia. Contractions and relaxations of the central piece were 

 sometimes noted. As the pseudopodia extend out radially farther 

 and farther, the tips become multiple, frequently come in contact and 

 fuse with neighboring ones to form a plasmodial network and sheet 

 back of the advancing tips or pseudopodia. In the course of an hour 

 or so, when most of the little chunk at the center has gone out into 

 the thin plasmodial net and sheet, some of the advancing ends become 

 retracting ends and the piece begins to migrate. Most of the active 

 plasmolets ultimately arrive at the periphery of the thin drop. 

 Whether this is due to some chemotactic response (Coman, 1940) , 

 or to chance trapping is unknown. During the course of a day the 

 pieces undergo many changes of form, and the small ones some- 

 times fuse to form larger ones and sometimes the larger ones divide. 

 The smallest simple active pieces that have begun to migrate 

 show in the course of an hour or two an organization that is much 

 like that of an ameba in its fundamental aspects. They consist of 

 a fluid endoplasm, the plasmosol and a tubular body with a thick 

 gel wall, the plasmogel, which continues into a simple thick-walled 

 posterior end and a broad fan-shaped transition zone, which termi- 

 nates in a lobulated crescentic anterior end with numerous pseudo- 

 podia. The locomotion of one of these small pieces of plasmodium 

 is in general very much like that of the ameba, except for the 

 rhythmic reversals of the endoplasmic flow, the complications of the 

 transition zone, and many little minor solations and gelations which 

 frequently give rise to many very small temporary streams of endo- 

 plasm which connect with channels and tubes. Contraction and par- 

 tial solation of the posterior part of the gel layer forces the endoplasm 

 forward through the tube and channels to the anterior end, where it 

 forces out pseudopodia at weak places and builds forward the Plas- 

 modium at their bases. After about thirty seconds, gelation sets in 

 at the anterior end; the resulting contractile tension there, together 

 with partial solation reverses the endoplasmic flow and expands the 

 posterior weakened end. After about thirty seconds, gelation at the 



