ANIMALCULES. 



715 



the highest animals, are but specialisations of this simple dividing up of 

 living cells. 



The Amoeba has been described somewhat fully, as a simple type of the 

 Root-footed animals. Many different kinds of Amcebse have been distin- 

 guished, varying in the characters of the pseudopodia and in other respects, 

 but they all agree in being single cells of granulated protojlasm, containing 

 a nucleus, and moving and feeding by means of pseudopodia. 



In the group next above the Amoebae, the Foraminifera, the protoplasm 

 of the central body is no longer naked. The animal assimilates from the 

 water in which it lives the necessary material for 

 surrounding itself with a chitinous or shelly covering, or The Foraminifera. 

 perhaps it utilises its own waste products for this purpose. 

 This shell, in some of the Foraminifera, is merely a delicate case within 

 which the soft body lives. In others, grains of sand, or sponge spicules are 

 obtained from without and embodied in the shell. 



For the purposes of movement, the animal sends out pseudopodia into the 

 surrounding water through the openings in its shell. The Foraminifera have 

 been divided into the Perforate and the 

 Imperforate, according as the pseudopodia 

 protrude through small openings scattered 

 all over the surface of the shell, or through 

 only one or two large openings. The shells 

 depicted in Fig. 3 are those of Perforate 

 Foraminifera, while in Fig. 2 we have an 

 Imperforate form, the egg-shaped Gromia. 

 In this latter, the protoplasm streams out 

 at one aperture, breaks up into numberless 

 fine threads which, here and there, run 

 together, forming thicker patches. The 

 whole surface of the simple shell has also 

 become covered with a thin layer of 

 protoplasm. If any small plant cell or 

 other particle suitable for food touches one 

 of the pseudopodia, other threads flow 

 together round it, and it is slowly drawn in 

 towards the aperture and passed into the 

 body. Such particles of food can often be 

 seen, as in the illustration, within the body 

 of a Gromia. 



The shells of the Perforate Foraminifera 

 are very varied in form. Sometimes they 

 consist of many chambers, for the proto- 

 plasm, as it grows, has not room in the 

 one little chamber with which it at first surrounds itself, and adds another 

 from time to time, each chamber, however, remaining in communication with 

 the last by means of one or more minute apertures through which a thread 

 or threads of protoplasm pass. The inner protoplasm can also stream out 

 in all directions through the perforations in the sides of the shell. 



A few of the many forms assumed by the shells of such Foraminifera 

 are given in Fig. 3. Some are more or less flattened, like coins, and have 

 therefore been called Nummilites(Fig.3, A) ; others are flask-shaped (C); others 

 again closely resemble the shells of the Ammonite or the Nautilus (B) ; in fact, 



Fig. 2. -GROMIA OVIFORMIS. 



