PROTOZOA 



3 



The granular endoplasm contains round watery spaces called 

 vacuoles, and some of them contain food in process of digestion 

 and are called food vacuoles. In fresh-water conditions a 

 special vacuole is seen which attains a large size and suddenly 

 disappears, but only to reappear in the same place. This is the 

 contractile vacuole. With the addition of dilute salt solution 

 it gradually ceases to act, and an Amoeba from salt water may 

 not, and usually does not, have a contractile vacuole at all. 



Ectoplasm 

 Endoplasm 

 Contractile vacuole 



Inner coat 

 Outer coat 

 Hucous coat 



FIG. 1. Amoeba proteus, free and encysted, the latter after Carter. In the 

 former the movement is upwards and to the right. The pseudopodia 

 are being produced anteriorly and are being withdrawn posteriorly. A 

 diatom has been taken in as food, and food and other vacuoles are present 

 in the endoplasm. 



This goes to indicate that in fresh- water conditions the water 

 imbibed through osmotic pressure tends to be excessive and 

 has to be regularly discharged. 1 



Among the primitive granules which are so numerous in 

 the endoplasm other granules may be observed of different 

 form and size. According to their appearance and reaction 

 these have been found to be either food particles reduced to a 

 small state by digestive processes or products of an excretory 

 nature. Small globules of fat have also been proved to be 

 present in some cases. 



1 1910. Zuelzer, Archiv fur Entwicklungsmech. der Organismen, Bd. 29, 

 p. 632. 



