2 THE PEOTOZOA 



B. Structure. 



The whole body is a naked mass of protoplasm, which is 

 of two kinds. 



1. The ectosarc is the clear substance forming the denser 



outer layer. 



2. The endosarc is the granular and more fluid central 



portion. Its flowing movements, which accompany 

 the protrusion and retraction of the pseudopodia, are 

 rendered obvious by the granules contained in it. 



Within the endosarc make out the following structures. 

 a. Vacuoles are spaces filled with fluid, which is less 



PV 



FIG. 1. Amoeba, (c. H. H.) 



EC, ectosarc. EN", endosarc. F, food-vacuole. N", nucleus, P, pseudopodium. 

 PV, pulsating vacuole. 



dense than the surrounding protoplasm. They 

 contain in many cases foreign particles taken in 

 as food. 



b. The pulsating vacuole is a space filled with a 



watery fluid. It is fairly constant in position, 

 and pulsates rhythmically. More than one may 

 be present. Time its pulsations. 



c. The nucleus is a spherical or ovoid body denser 



than the rest of the endosarc and highly refrac- 

 tive. During life it is not easily seen, but it is 

 rendered obvious by killing the animal with 

 acetic acid (1 per cent.), or by staining with 

 magenta. More than one may be present. 



