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Univerdty of California Puhlications in Zoology ["^'ol. 20 



balloon-like pseiulopodia (pi. 43, fig. 2; fig. B, 1) are more common. 

 The endopla.sm may move into and fill the pseudopodia formed when 

 the amoeba is thus attached, but more commonly the pseudopodia are 

 retracted or a p.seudopodium may be partly filled with endoplasm and 

 the remaining portion retracted. 



In accordance with the gel-sol theory of pseudopodial formation 

 (Hyman, 1917), this hyaline ectoplasm after protrusion represents 

 a gel and the more vacuolated endopla.sm a sol, each of which is 

 reversible, one into the other, as protrusion, advancement, or retraction 

 occurs. 



Fig. B 



Free-hand sketch, showing foimation, while attaclied, of pseudopodia of 

 Councilmania miiris from rat. 



In the formation of a pseudopodium, solution of the ectoplasm 

 occurs at the initial point of formation. This liquid sol spreads out- 

 ward and forward, its outer surfaces forming a gel, a.s contact occurs 

 with the medium of the environment. The liquid endoplasm then flows 

 in and occupies the space between these gelated layer.s. In retracting 

 a pseudopodium, the gelated ectopla.sm is gradually reversed to a sol 

 state. 



In this discu.ssion it is preferred to describe the protoplasm as 

 separated into two layers, the ectoplasm and endoplasm, rather than to 



