SECTION I.— PHYLUM PROTOZOA 

 1. THE RHIZOPODA 



The simplest members of the animal kingdom are for the 

 most part, too small to be visible without the aid of a micro- 

 scope, or at least so small as to appear to the unassisted eye 

 as extremely minute specks, not distinguishable, unless in 

 unusually active movement, from small particles of non-living 

 matter. Representatives of this class of simple minute ani- 

 mals are to be found living under a variety of different con- 

 ditions ; they are abundant in fresh water, running or 

 stagnant, and they are equally numerous in the sea, while 

 they are also to be found* living in the fluids of cavities in 

 the bodies of higher animals. An example which will serve 

 to illustrate some of the main features of the class is the 

 Proteus animalcule or Amoeba. Amceba (Fig. i) is some- 

 times to be found by searching with the aid of the micro- 

 scope in water from stagnant pools. To the unpractised 

 beginner it is a difficult task to discriminate between the 

 microscopic particles of non-living matter which form the 

 main part of the sediment at the bottom of such a pool — 

 debris of animals, vegetable or mineral nature — and the 

 object of which he is in search. Numerous minute bodies 

 will doubtless be seen which their active movements among 

 the motionless particles show to be endowed with life. But 



