32 INVERTEBRATE ANIMALS. 
Ameba wraps a pseudopodium round it, and then withdrawing 
the pseudopodium, lodges the nutrient particle securely in the 
substance of the body. It follows from this that the As@ba has 
no permanent mouth—no aperture, that is, which is especially 
employed in the admission of food. Any part of the surface can be 
pushed out into a pseudopodium, and therefore any part of the 
surface can be extemporised into a mouth. The process of taking 
food, in fact, in the Ameba, has been aptly compared to thrust- 
ing a stone or any other solid body into a lump of dough. The 
central portion of the body of the animal is softer and more fluid 
than the outer layers, and the particles of food, on reaching this 
point, undergo a sort of digestion, and are subjected to a species 
of movement or rotation in the interior of the animal. Each 
Fig. 4.—Amoebea. A, Small A7zebe developed in organic infusions, greatly mag- 
nified. B, Ameba princeps; n Nucleus; ¢ Contractile vesicle; wv Region of 
the body where indigestible matters are thrust out. 
particle of food, in the process of being taken into the body, 
usually carries with it a little drop of water; and in this way 
a number of clear spaces are formed, which are usually quite 
round, and look like distinct cavities. These spaces are called 
“vacuoles ;” but they are not distinct organs of any kind, though 
formerly regarded as distinct stomachs. Having undergone 
digestion, any portions of food which may be indigestible or in- 
soluble are simply thrust out again through the walls of the 
body. This appears to be effected at one particular part of the 
body; but there is no permanent aperture for the purpose. 
There are no distinct vessels which serve to convey the nutri- 
tive fluid derived from the digestion ; but there does appear to 
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