AMOEBA 135 



round it. It is evident that the walls of the death-chamber, 

 formed of fused pseudopodial processes, were originally part 

 of the external layer or ectoplasm, and that in enclosing the 

 Cyclidium or other prey they have become internal, and are 

 eventually merged into the inner substance, or endoplasm, of 

 the Amoeba. Thus ectoplasm can become endoplasm and 

 vice versa. It would not, however, be correct to say that 

 all Amoebae consist of naked protoplasm without any external 

 limiting coat. Amoeba bi-nucleata, so named because it has 

 two nuclei, is a form with a distinct though very thin pellicle 

 outside the external alveolar layer, and this pellicle may be 

 made evident by certain dyes. Pelomyxa palustris, a very 

 large and rather peculiar Amoeba, is covered all over with 

 minute non-vibratile hair-like appendages ; and Amoeba villosa 

 has a tuft of similar appendages at one end of its body, 

 pseudopodia of simple form being formed only at the opposite 

 end. 



It has been demonstrated that the contents of the food- 

 vacuoles, at the time of their formation, are acid, and eventu- 

 ally they exercise a solvent action upon proteid substances, 

 but not, it would seem, upon starches and fats. It is most 

 probable that the fluid contents of a food-vacuole are a 

 special secretion of the protoplasm, containing a ferment or 

 enzyme, which has an action analogous to that of the gastric 

 secretion of higher animals. The proteid morsel enclosed in 

 a food-vacuole is gradually dissolved, and disappears, only a 

 small granular residue remaining. This residue is eventually 

 rejected together with other non-nutritious substances that 

 have been taken in, as it were, accidentally. There is no 

 special aperture for the ejection, as there is none for the 

 ingestion of solid matter. One may say that the Amoeba 

 flows away from its indigestible contents, leaving them 

 behind. 



Since Amoebae live in muddy and sandy bottoms amidst 

 all sorts of inorganic non-nutritious grains and fragments, it is 

 clear that they must exercise some sort of selection in ingest- 

 ing solid matter ; for if they did not they would take in every 

 particle of convenient size that they meet, and they do not. 

 Moreover an Amoeba living in water that contains numerous 

 diatoms of relatively large size may be seen to engulf a 

 number of these apparently inconveniently large objects 



