ON PELOMYXA VIEIDIS. 365 



hyaline protoplasm protruded at some one spot, leaving all its 

 contents behind, and then spread out laterally, while a sharply 

 defined line seems to mark the original boundary ; this line 

 afterwards disappears, giving one at first the impression that 

 the protoplasm, which has, so to speak, overflowed the original 

 boundary but remained in contact with it, is separated from the 

 rest of the protoplasm, except at the spot whence it actually 

 protruded, by a sort of pellicle, which is subsequently dissolved. 

 Gruber^ has figured such an appearance for P. villosa, and 

 says, " Wenn an einem ausgetretenen Protoplasmafortsatz 

 die Vacuolen und die Kornchen einige Zeit durch eine scharfe 

 Linie von der Sarkode getrennt bleiben, so beruht dies darauf 

 dass das Pseudopodium durch Zusammenfliessen des Plasmas 

 ueber diese Stelle hinentstand,und dass die feine peripherische 

 Schicht von Protoplasm a, welche vorher die Grenze gegen das 

 umgebende Medium bildet, und welche jetzt von der Masse 

 des Pseudopodiums umflossen wird noch eine Zeit lang er- 

 halten bleibt ;" and regards this as further evidence of the 

 existence of a relatively hard cuticular layer or pellicle formed 

 by the action of the water, a view which the same author put 

 forward on a previous occasion.^ 



I cannot accept this interpretation of the facts. I do not 

 believe that the hyaline protoplasm is protruded at one spot 

 only, and that there is lateral displacement of its particles ; 

 the undulating appearance is chiefly caused, like other wave 

 movements, by extrusions and retractions in a radial direc- 

 tion. The appearance of the boundary line may be explained 

 by careful focussing, the line being at some slightly diff'erent 

 level from the protruding protoplasm, and its disappearance 

 being due to a subsequent protrusion at that particular level. 

 I am not at all sure liow far the existence of any such pellicle 

 as Gruber describes is in accordance with the views as to the 

 relation of protoplasm to imbibition water.^ 



If the density of the surrounding medium is increased, as 



' ' Zeit. f. w. Zool.,' Bd. xli, 188i, pi. xiii, fig. 2, and p. 190. 

 - 'Zeit. f. w. Zool.,' Bd. xxxvi, 1882, p)). 457—469. 

 ' See Engelmann ou " Protoplasmic Movement," in this Journal, vol. xxiv, 

 1884, p. 390. 



