268 THE FOOD OF ANIMALS 



interior of the body through the delicate membrane by which it is 

 invested. 



Rhizopods (see vol. i, p. 489). — These are animalcules of 

 lower grade than the preceding group, for the body is not 

 covered by a membrane conferring a definite shape, and is de- 

 void of the specialized threads (cilia and flagella) which, as we 

 have just seen, play such an important part in the feeding of 

 higher Protozoa. The simplest and at the same time most in- 

 structive example is the Proteus Animalcule {A7nceba), a micro- 

 scopic creature found in all sorts of places, especially on mud and 

 water-plants in ponds and ditches. Its body is a mere particle 

 of living substance (protoplasm), semifluid in consistency, and 

 continually altering its shape when the animal is in an active 

 healthy state, a circumstance which has suggested both the 

 common and scientific names. On watching a living amceba, 

 which has been placed in a drop of water under the microscope, 

 its body will be observed to flow out from time to time into 

 bluntish lobes, which, however, are in no sense permanent struc- 

 tures, for they are sooner or later drawn back so as to form 

 part of the general body. Each such lobe is somewhat inappro- 

 priately called a " false-foot " (pseudopod), and its use is to help 

 in locomotion and the taking in of food. Amceba possesses 

 neither mouth nor internal digestive cavity, for in the absence of 

 a firm bounding membrane nutritive particles can be taken in 

 at any point, being engulfed by the pseudopods. The body, 

 so to speak, flows round the food, which is of varied nature, 

 consisting of microscopic plants and animals, together with 

 organic particles of different kinds. With these a good deal of 

 water is taken into the body, and food-containing globules (food- 

 vacuoles) result, much as in a Slipper Animalcule or Bell Animal- 

 cule (see vol. i, p. 492). These move round in the interior of the 

 animal and are gradually digested, the innutritlous or undio-ested 

 parts being cast out of the body wherever most convenient. It 

 might almost be said that an amoeba flows away from the re- 

 mains of its meals. The Proteus Animalcule has been observed 

 feeding upon certain lowly green plants {cUgce) much longer than 

 itself, and the tactics pursued in order to get these entirely within 

 the body are extremely interesting (fig. 472). There is, of course, 

 no difficulty in flowing round one end of such a plant, and the 

 next move is for a pseudopod to be pushed along it, and then 



