AMCEBA. 85 



three great classes is marked by the predominant, and not by 

 the exclusive occurrence of the Rhizopod-like, or the Infusorian- 

 like, or the Sporozoon-like phase of cell life. Many have a 

 skeletal framework of lime, flint, or other material, while 

 within the cell there is a special kernel or nucleus, or there 

 may be several. There are also other less constant structures. 

 A Protozoon multiplies by dividing into two daughter units, 

 or into a large number ; and two individuals often unite, 

 temporarily or permanently, in conjugation, which is analogous 

 to the union of ovum and spermotozoon in higher animals. 

 A few types, instead of remaining single cells, form by 

 division or budding loose colonies, taking a step, as it were, 

 towards the Metazoa. 



First Type of Protozoa — Amceba. 



Amoeba, a type of Rhizopods, especially of those in which 

 the outflowing processes of living matter {pseudopodia) are 

 blunt and finger-like (Lobosa). 



Description. — Amoeba proteus and some other species are 

 found in the mud of ponds ; A. terricola occurs in damp 

 earth. Some are just large enough to be seen with the 

 unaided eye. The diameter is often about one-hundredth 

 of an inch. Each is like a little sac of jelly, and glides 

 over the surface of stone and plant by protruding and 

 retracting the pseudopodia. As they move the shape con- 

 stantly changes, whence the old (1755) name of "Proteus 

 animalcule." Round the margin, which may show an 

 apparent radial striation, the cell-substance is firmer and 

 clearer than it is in the interior, where it is more fluid, but 

 contains very abundant granules, some of which are of 

 a proteid, and others of a fatty nature. According to 

 Professor Ray Lankester, the formation of pseudopodia is 

 due to the outflowing of the central fluid substance at 

 places where the outer pellicle has been temporarily 

 ruptured. In the centre of the cell lies the usually single 

 nucleus, but Amoeba princeps has numerous nuclei. The 

 food consists of minute Algae, such as diatoms, or of 

 vegetable ddbris. It is surrounded by the finger-like pro- 

 cesses, and engulfed along with drops of water, which form 

 food vacuoles in the cell-substance. After the digestible 



