SECTION I. 



THE GENERAL STRUCTURE AND PHYSIOLOGY 

 OF ANIMALS 



1. Amceba. 



If we examine under the microscope a drop of water containing 

 some of the slimy deposit which collects at the bottom of pools of 

 rain-water and in similar situations, we occasionally find it to 

 abound in microscopic life ; and among the minute moving creatures 

 in such a drop we frequently find examples of a remarkable' or- 

 ganism — the Amceba or Proteus Animalcule (Fig. 1). This is 



a little particle of irregular 

 shape, which we should be 

 likely, on a cursory examina- 

 tion, to put down as motion- 

 less ; it appears somewhat like 

 an irregular particle of some 

 colourless glass-like substance 

 with a more granular central 

 portion. If, however, we make 

 an exact drawing of the out- 

 line of the Amoeba, and, after 

 an interval, compare the draw- 

 ing with the original, we find 

 that the drawing appears no 

 longer to represent what we 

 see ; a change has taken place 

 in the shape of the Amoeba ; 

 and careful observation shows that this change is constantly going 

 on : the Amoeba is constantly varying in shape. This change is 

 effected by the pushing out of projections or processes, called 

 .pseudopods {pscl.), which undergo various alterations of size 

 and shape, and may become withdrawn, other similar processes 

 being developed in their place. At the same time careful 



Fig. 1. — Amoeba proteus, <a living specimen. 

 c. vac. contractile vacuole ; nu. nucleus ; 

 psd. pseudopods. (From Parker's Biology, 

 after Gruber.) 



