152 THE AMERICAN MONTHLY [July, 



of moistened writing paper near to the drop, apply a cover glass so 

 that one edge rests on the paper. I have written may because AnKX'bae 

 are very uncertain beings, and one may go for a long time without meet- 

 ing with any, and at other times have a rich supply. When these 

 fail the student, the white blood corpuscles will do very well as a sub- 

 stitute, and they can always be obtained without much difficulty. It is 

 possible that some Amoebae at least are only stages in the life-history of 

 other organisms. 



II. Size. — This varies — the average diameter being 5 m.m. But it 

 must be remembered that the different diameters of an Amoeba are 

 not alwavs the same length. It may be at times much broader or longer 

 in one direction than in another. 



III. General Structure. — It consists of an irregular mass of proto- 

 plasm, but the protoplasm is to some extent difterentiated. for nearer 

 the centre of the Amoeba it is more granular and fluid than near the 

 circumference ; hence, we call the inner, more granular, more fluid 

 part, the endosarc (£/'J«v= within, /7«/'r=flesh) . the outer, less gran- 

 ular and more solid part, the ectosarc (£zr«v=without) . Yet. Amoeba 

 is without a distinct w^all or membrane. Its ectosarc is only a filmy, 

 rather more condensed part of the protoplasm of which the Amoeba 

 is made up. Within the endosarc is a more condensed part of the pro- 

 toplasm, the nucleus or endoplast. At times within this the student 

 may recognize a rounded granule, the nucleolus or endoplastule (ula=a 

 diminutive ending). 



IV. Forms of Aincebce. — Some Amoebae have shell-like coverings. 

 At times they become surrounded by a sac not unlike the gelatinous in- 

 vestment seen in the still or zooglcea stage of bacteria. Then they are 

 said to be encvsted. Lastly, another special form of this organism is 

 occasionally seen, in which the distinction between ecto- and en- 

 dosarc is but little marked, and the granular structure is not so evident 

 (Amceda radiosa) . 



b. DIGESTION'. 



The food of the Amoeba is mostly vegetable. Low% minute forms 

 of algas, water plants low in the scale of vegetable life, are the staple 

 comestible. These are taken in by a remarkable mechanism. If a 

 particle of food is near an Amoeba, that part of the body of the latter 

 which is nearest to the former is protruded as a pseudopodium. This 

 touches the food particle which adheres to it, and as the pseudopodium 

 shortens and is withdrawn to the body of the Amoeba, once again the 

 food goes with it, and is slowly drawn into the endosarc. There is no 

 mouth. There is not even a defined region that is to serve always as 

 the temporary mouth. An\^ part of the body may be pushed out and 

 may seize food. This latter, once within the endosarc. passes slowly 

 through the body of protoplasm, growing smaller and smaller, and, 

 after awhile, such portion of it as is not used by the Amoeba is extended 

 at an indefinite point on the general surface of the body. It will be 

 noticed that here is an advance on the ingestion of food by bacteria, for, 

 in these last, all the surface is concerned ; but in the Amoeba only a 

 part of the surface is concerned in the taking in of any special food 

 piece. This part may be at anv region. There is a clear advance in 

 diflerentiation. Amreba gets its organic food-stufl" readv made. The 

 tiny vegetable things it eats have beforehand fashioned out ot mineral 



