Viscosity Changes of Protoplasvi 181 



protoplasm which is evidently in the gel state. This holds back the 

 granular endoplasm which piles up behind it, but seems to permit, 

 as Mast has suggested for the ameba, the hyaloplasm to filter through 

 its pores to form the hyaline cap. This rather thin, granular, plas- 

 mogel membrane often has a smooth outline bordering the base of 

 the hyaline cap, and its granular vacuoles are at rest. This membrane 

 may persist, or a small local break or two may occur and small 

 streams of granules suddenly pour through them into the cap. Then 

 the entire membrane may give way and the cap rapidly fill with 

 granules and all traces of the gel layer disappear. The anterior end 

 does not possess a thick, tough gel layer such as one can see and 

 manipulate at the posterior end and tube region. There is much 

 more protoplasm at the anterior end and in the anterior part of the 

 broad transition zone than in the tube and posterior end, but it seems 

 to be less viscous. With each forward flow of the endoplasm pro- 

 duced by the contraction of the gel layer at the posterior end and 

 on the tube, this mushy protoplasm is pushed forward within the 

 bulging boundaries of a rather thin gel layer of the lobes. At the 

 weakest areas, the pseudopods and hyaline caps form and bulge out 

 still more. Forward flow is probably much impeded and slowed by 

 the friction in the relatively large number of small and minute ter- 

 minal channels. The forward flow and expansion cease with the 

 increase in the viscosity and partial gelation of the lobes and of the 

 pseudopods. One can detect these changes by the absence of the flow 

 and the absence of Brownian movement of the granular vacuoles. 

 This is probably not a very viscous gel, but there are many such 

 ends. It seems probable that height of gelation is synchronized with 

 a weakening of contractile tension at the posterior end so that the 

 contractile tension which now develops at the anterior ends as a 

 result of the increased viscosity and gelation reverses the endo- 

 plasmic flow. 



During the anterior contraction period each pseudopod contracts 

 and shortens. They do not always contract simultaneously, and an 

 occasional new one may form. The amount of contraction usually 

 falls short of the previous gain so that there results a net forward 

 gain with each cycle. The contraction usually involves more than 

 the pseudopodal tip and there may be a considerable amount of 

 retraction of the whole lobe. During the contraction there is a 

 backward flow of the endoplasm. Small, more-or-less temporary 

 streams from neighboring tips join to form larger and larger chan- 

 nels which unite and join to form the tubes. A large part of the 



