158 PHYLUM PROTOZOA 



Class : Sarcodina. Order : Rhizopoda 

 AMCEBA 



The amoeba is a jellylike, single-celled animal which may be 

 found in stagnant water attached to submerged objects, or in 

 bottom sediment ; it is also often found in moist, damp places 

 which are not under water. There are many species, the largest 

 being within the range of the unaided vision, the smallest species 

 requiring high powers of the microscope to detect. Among the 

 common species of amoeba are Amoeba proteus, a large, often 

 active form with long pseudopodia, Amoeba verrucosa, a large, 

 sluggish form with very short pseudopodia, Amoeba Umax, a 

 small form which flows along without definite pseudopodia, and 

 Amoeba radiosa, a small, star-shaped form with slender, radiating 

 pseudopodia. 



Mount on a slide a drop of water with sediment or scrapings 

 from a submerged leaf or stick containing amoebas, and find one. 

 Observe its shape and granular appearance. From time to time 

 the shape of the body changes by the thrusting out of projections 

 called pseudopodia. Observe the formation of pseudopodia. 



Exercise 1. Draw several outlines of the animal showing its shape at 

 different times. 



Observe the structure of the body. The protoplasm forming it 

 will be seen to be divisible into two layers, the ectosarc and the 

 entosarc ; the former is the clear, transparent layer which forms 

 the periphery of the body ; the latter is the granular, translucent 

 mass which forms the remainder of it. The ectosarc is of firmer 

 consistency than the entosarc, and its outer surface forms a deli- 

 cate cuticula. When a pseudopodium begins to form, it consists 

 at first of ectosarc alone, but entosarc finally enters it as it grows 

 larger. The entire body will often flow into a single pseudopo- 

 dium, in which case the animal flows in that direction. When 

 this happens the ectosarc of the hinder portion of the body will 

 be seen to wrinkle as the entosarc flows away from it. 



Observe the granular nature of the entosarc and the flowing of 



