THE HELIOZOA 17 



clearer coarsely vacuolated ectoplasm, and a less transparent spongy 

 or feebly vacuolated endoplasm, containing a centrally placed nucleus 

 (Fig. 2(1), d). The ectoplasm is normally so crowded with vacuoles 

 that it is reduced to a mere system of septa, and to a thin layer form- 

 ing the cortex of the radial pseudopodia. During the ingestion of 

 food, however, an aggregation of ectoplasm takes place, forming a 

 short, blunt amoeboid projection by which the food is engulfed, and 

 in which a digestive food-vacuole is formed (Fig. 2(1), a). The ecto- 

 plasm usually contains a number of bright, highly refringent granules, 

 remarkably uniform in diameter, which are carried from one region 

 to another by streaming movements of the protoplasm ; thus they 

 may often be seen streaming to or from the apex of a radial pseudo- 

 podium, or towards the apex on one side and away from it on the 

 other. The number of these granules is said to increase with 

 increased nutrition, but their chemical nature is quite unknown. 



FIG. 2. 



1, Actinophrys sol, Ehrb., x 800; o, food-particle lying in a large food-vacuole; 6, deep- 

 lyiii^' finely granular protoplasm ; c, axial filament of a pseudopodium extended inwards to the 

 nucleus ; d, the centrally placed nucleus ; e, contractile vacuole ; /, superficial, much-vacuolated 

 protoplasm. 2, Clathrulina elegans, Cienk., x 200. 3, Heterophrysmyriopoda, H. and L., x 660 ; 

 a, nucleus ; 6, clearer protoplasm surrounding the nucleus ; e, the peculiar felted envelope. 

 4, Rhaphidiophrys pallida, V. E. Schultze, x 430 ; a, food-particle ; b, a contractile vacuole (?), 

 the nucleus is probably represented by the circular shaded body lying below 6 ; c, a food-particle ; 

 rf, the centrosome. The tangentially disposed spicules are seen arranged in masses at the 

 surface. 5, Acanthocystis turfacea, Carter, x 240 ; a, probably the centrosome ; b, clear pro- 

 toplasm around the centrosome ; c, more superficial protoplasm with vacuoles and xanthellae ; 

 d, coarser siliceous spicules ; e, finer forked siliceous spicules ; /, finely granular layer of 

 protoplasm. The long pseudopodia stretching beyond the spicules are not lettered. 6, biflagellate 

 "flagellula" of Acanthocystis acideata; a, nucleus. 7, Flagellula of Clathrulina elegans; , 

 nucleus ; b, granules of uncertain composition. 8, Astrodisculus radians, Green , x 320 ; o, red- 

 coloured fatty globule ; 6, peripheral homogeneous envelope. (From Lankester, after various 

 authors.) 



The endoplasm is rarely vacuolated, and the bright refringent 

 granules are absent from it. 



In a normal pseudopodium we can distinguish (1) a cortical 

 layer, and (2) an axial filament. The cortical layer is continuous 

 with the general ectoplasm at the base of each pseudopodium ; it is 

 irregular in thickness, and may by a streaming movement become 

 aggregated into amoeboid droplets of relatively large size during 

 the seizure of prey (Fig. 2 (3)). The effect produced upon infusoria, 

 small rotifers, and other ciliated organisms by contact with the 

 pseudopodia is a marked paralysis, which has led many observers, 

 from Ehrenberg onwards, to assume that some poisonous substance 

 is formed by or contained in the cortex; but direct chemical 

 evidence of this is wanting. The axial filament is a clear homo- 

 geneous thread, which runs from the apex of a pseudopodium 

 through the substance of the body, to end in a central dilatation in 

 contact with the nuclear membrane. When a pseudopodium is 

 withdrawn, its axial filament disappears, and cannot be demon- 

 strated by staining reagents ; in the living animal it is more easily 



