PROTOZOA OR SIMPLEST ANIMALS. 6 



Food may be taken in and the remains ejected at any point of High Wall 

 the body, but sometimes only over more or less definite areas. The ^^^® 

 body of the animal is usually crowded with food-balls, shells of Gallery. 

 Diatoms, cells of green algae, &c. 



The protoplasm of the body, with the exception of a thin, clear, 

 outer layer, is granular ; at one part (Fig. 1) is seen a discoid, denser 

 portion of protoplasm, known as the "nucleus." There is also 

 present in the interior of the body a clear spherical vesicle— the 

 " contractile vacuole " — which slowly expands and rather suddenly 

 collapses and disappears, reappearing at the same spot and going 

 through the same cycle. The contractile vacuole is probably an 

 organ for the excretion of waste products. The animal reproduces 

 itself by dividing into two, this process being preceded by division of 

 the nucleus, each half of the Amoeba becoming a distinct individual. 



Classification. 



The Protozoa are divided into two great sections — the Gymno- 

 MYXA or Rhizopoda, and the Corticata or Infusoria. 



In the first section, the protoplasm of the cell is homogeneous 

 throughout, but in the second the superficial layer is firmer than 

 the more fluid interior portion. 



The Gymnomyxa, in their adult phase, move about and obtain 

 their prey by means of pseudopods. The Corticata are provided 

 with flagella or cilia. A classification of the Protozoa (after Prof. 

 Lankester, Encyc. Britannica) is given in the " Explanation of 

 Plates " in the Case. 



GYMNOMYXA (RHIZOPODA). 



For simplification, the Gymnomyxa are here divided into four 

 groups : — 



I. Lobosa, with lobose pseudopods. 



II. Heliozoa, with fine radiating pseudopods. 



III. Foraminifera, in which main trunks of pseudopods branch 

 out into a fine network, and with a shell usually composed of carbonate 

 of lime. 



IV. Radiolaria, with a " central capsule," with fine radiating 

 pseudopods, and usually with a shell of silex or horny acanthin. 



B 2 



