124 PROTOZOOLOGY 



movements, which was much extended by Hyman (1917). Hyman 

 considered that: (1) a gradient in susceptibility to potassium cyanide 

 exists in each pseudopodium, being the greatest at the distal end, 

 and the most recent pseudopodium, the most susceptible; (2) the 

 susceptibility gradient (or metabolic gradient) arises in the amoebae 

 before the pseudopodium appears and hence the metabolic change 

 which produces increased susceptibility, is the primary cause of 

 pseudopodium formation; and (3) since the surface is in a state of 

 gelation, amoeboid movement must be due to alterations of the col- 

 loidal state. Solation, which is brought about by the metabolic 

 change, is regarded as the cause of the extension of a pseudopodium, 

 and gelation, of the withdrawal of pseudopodia and of active con- 

 traction. Schaeffer (1920) mentioned the importance of the surface 

 layer which is a true surface tension film, the ectoplasm, and the 

 streaming of endoplasm in the amoeboid movement. 



Pantin (1923) studied a marine limax-type amoeba (Fig. 44, 6) and 

 came to recognize acid secretion and absorption of water at the place 

 where the pseudopodium was formed. This results in swelling of the 

 cytoplasm and the pseudopodium is formed. Because of the acidity, 

 the surface tension increases and to lower or reduce this, concentra- 

 tion of substances in the "wall" of the pseudopodium follows. This 

 leads to the formation of a gelatinous ectoplasmic tube which, as the 

 pseudopodium extends, moves toward the posterior region where the 

 acid condition is lost, gives up water and contracts finally becoming 

 transformed into endoplasm near the posterior end. The contraction 

 of the ectoplasmic tube forces the endoplasmic streaming to the 

 front. 



This observation is in agreement with that of Mast (1923, 1926, 

 1931) who after a series of carefully conducted observations on 

 Amoeba proteus came to hold that the amoeboid movement is 

 brought about by "four primary processes; namely, attachment to 

 the substratum, gelation of plasmasol at the anterior end, solation of 

 plasmagel at the posterior end and the contraction of the plasmagel 

 at the posterior end" (Fig. 46). As to how these processes work, 

 Mast states: "The gelation of the plasmasol at the anterior end ex- 

 tends ordinarily the plasmagel tube forward as rapidly as it is broken 

 down at the posterior end by solation and the contraction of the 

 plasmagel tube at the posterior end drives the plasmasol forward. 

 The plasmagel tube is sometimes open at the anterior end and the 

 plasmasol extends forward and comes in contact with the plasma- 

 lemma at this end (Fig. 47, a), but at other times it is closed by a 

 thin sheet of gel which prevents the plasmasol from reaching the 



