1903 



British Field Zoology 



171 



distinguish the amoebae amongst the diatoms, infusoria, and flocculent 

 vegetable matter, all of which are more conspicuous than our quarry. 

 There are several species of Amoeba, and they vary greatly both in size 

 and activity. The large ones are generally the more actively moving ; 

 the smaller, sluggish. Under the I -inch objective a large one will appear 

 about y 2 inch in diameter ; a small one less than ^ inch. The animal 

 is colourless and formless. The substance is somewhat of the con- 

 sistency of white of egg, and it is continually changing shape by flowing 

 over itself, hence the name from d/Aoi/Jos = changing. 



When an Amoeba wishes to advance in any direction it pushes out- 

 wards a portion of its body-substance (protoplasm) as a blunt finger-like 

 projection. The projection is called a pseudopodium ( = false-foot), and 

 the whole class to which the Amoeba belongs is named Rhizopoda 

 ( = root-footed animals)). The more fluid inner portion of the body then 

 flows into the advanced pseudopodium, which is thereby distended more 



Fig- 5- 



and more till the whole body-substance has left its original position and 

 now occupies the position taken up by the advanced pseudopodium. In 

 this way the Amoeba performs one of its functions of relation — loco- 

 motion. Put into few words, we may say that in this simple animal 

 locomotion is effected by the entire body flowing along from point to 

 point (fig. 5). 



In the higher animals we recognise as functions of relation the 

 phenomena associated with the sense-perceptions — sight, taste, touch, 

 smell, and hearing, and these we know to be performed by special 

 sense-organs — branches of the nervous system. It is hardly necessary 

 to point out that in the Protozoa — as unicellular organisms — there is no 

 nervous system. Nevertheless it is impossible to watch an Amoeba for 

 any length of time without perceiving that it is possessed of sensibility, 

 for (1) it avoids obstacles in its course, and (2) it selects its food. We 

 can only surmise that the protoplasm of the body is possessed of a kind of 

 diffused sensibility enabling it to perceive its relations to its environment. 



Just as the plan of locomo- 

 tion adopted by Amoeba is jf \ 

 the simplest imaginable, so ( & /S> 



also is its method of feeding — \ O -^ 

 the function of nutrition. V 



When the animal comes Fig. 6. 



across a particle of organic 



matter suitable for food it puts out two pseudopodia — one on each side 

 (fig. 6). These lengthen until they meet on the opposite side and 

 coalesce, when the body closes over the food. A small quantity of 



