3526 



THE LOWEST ANIMALS 



generally. found on the ooze of ponds, or the under surface of the leaves of aquatic 

 plants, but especially among conferva, in clear gently flowing water. When first 

 caught, the animal will appear as a tiny yellowish semitranslucent globular speck, 

 about one-hundreth of an inch in diameter; presently it becomes beaded with rounded 

 projections, some of which grow longer at the expense of others and of the body, 

 and may give off one or two branches. By the projection of these processes, or 

 pseudopods, the amoeba moves along in the direction of the longer ones. ' ' Some- 

 times," writes I^eidy, "the animal creeps onward in a flowing manner with com- 

 paratively simple cylindroid form, occasionally emitting a single pseudopod on one 

 side or the other. More commonly, in movement, it assumes a dendroid or palmate 

 form, or sometimes, diverging from the directly onward course, it becomes more 

 radiate in appearance. Not unfrequently it assumes more or less grotesque shapes, 



PROTEUS ANIMALCULE (highly magnified). 



in which almost every conceivable likeness may be imagined." The body of the 

 amoeba is full of granules, which render it semiopaque, with the exception of a thin 

 clear outer hyaline zone, and near the centre is a globular or discoid body, known as 

 the nucleus, composed of a denser protoplasm than that which surrounds it. Divi- 

 sion of an amoeba into two is preceded by division of the nucleus. Near the latter 

 is a clear spherical space the contractile vacuole which gradually expands, 

 rather suddenly collapses, and reappears at the same spot, the systole and diastole 

 being slow and continuous. The contractile vacuole contains a clear liquid, which 

 is expelled on the collapse of the vacuole. This organ probably serves the double 

 function of respiration and excretion. The amoeba is omnivorous, but is chiefly 

 vegetarian, and browses on tender leaves, or feeds on diatoms and other algae; it 

 surrounds the food particle or organism with the protoplasm of its body or of a 

 pseudopod, and the ingested particle sinks in, surrounded by a zone of water; fre- 



