110 



PROTOZOOLOGY 



lemma at this end (Fig. 45, a), but at other times it is closed by a 

 thin sheet of gel which prevents the plasmasol from reaching the 

 anterior end (6). This gel sheet at times persists intact for consider- 

 able periods, being built up by gelation as rapidly as it is broken 

 down by stretching, owing to the pressure of the plasmagel against 

 it. Usually it breaks periodically at various places. Sometimes the 

 breaks are small and only a few granules of plasmasol pass through 

 and these gelate immediately and close the openings (d). At other 

 times the breaks are large and plasmasol streams through, filling the 

 hyaline cap (c), after which the sol adjoining the plasmalemma gel- 



FiG. 45. Diagrams of varied cytoplasmic movements at the tip of a 

 pseudopodium in Amoeba 'proteus (Mast), g, plasmagel; he, hyaline cap; 

 hi, hyaline layer; pi, plasmalemma; s, plasmasol. 



ates forming a new gel sheet. An amoeba is a turgid system, and the 

 plasmagel is under continuous tension. The plasmagel is elastic and, 

 consequently, is pushed out at the region where its elasticity is 

 weakest and this results in pseudopodial formation. When an amoeba 

 is elongated and undergoing movement, the elastic strength of the 

 plasmagel is the highest at its sides, lowest at the anterior end and 

 intermediate at the posterior end, which results in continuity of the 

 elongated form and in extension of the anterior end. If pressure is 

 brought against the anterior end, the direction of streaming of plas- 

 masol is immediately reversed, and a new hyaline cap is formed at 

 the posterior end which is thus changed into a new anterior end. " 



Flagellar movement. The flagellar movement is in a few instances 

 observable as in Peranema, but in most cases it is very difficult to 

 observe in life. Since there is difference in the number, location, size, 

 and probably structure (p. 45) of flagella occurring in Protozoa, it 

 is supposed that there are varieties of flagellar movements. The first 

 explanation was advanced by Biitschli, who observed that the flagel- 

 lum undergoes a series of lateral movements and, in so doing, a pres- 



