I AMOEBA 3 



material (such as Calcium phosphate), some are drops of watery fluid 

 and these when they are of considerable size are known as fluid vacuoles. 

 Small bubbles of Carbon dioxide (gas vacuoles) are sometimes to be 

 recognized in other kinds of Amoeba but they are exceedingly rare, if 

 they occur at all, in Amoeba proteus. 



The ectoplasm differs from the endoplasm in that it is less fluid, 

 more highly refracting, without enclosed granules and of a clear glassy 

 appearance. It is usually very thin and its outer surface normally 

 covers itself with a thin coating of slime which is of importance in the 

 creature's movements. 



The nucleus is a dense, fairly solid, highly refracting body — colourless 

 like the rest of the protoplasm and showing a characteristic uniformly 

 mottled appearance. This mottled appearance is due to its being com- 

 posed of two different substances the one denser and more highly refracting 

 than the other. The former, consisting of a complicated mixture of 

 proteins which are specially rich in Phosphorus, is characterized by a 

 special affinity for certain stains or dyes. When the dead Amoeba is 

 subjected to the action of these stains this portion of the nuclear material 

 becomes stained specially deeply and the substance of which it is com- 

 posed has consequently been given the name chromatin to distinguish 

 it from the less deeply staining achromatin. 



Continued observation of living specimens of Amoeba brings out many 

 other points besides those already mentioned. The living Amoeba shows 

 almost constant movement — movement of a kind so characteristic that 

 although it occurs in various other animals it is known technically as 

 amoeboid movement. This movement consists in the pushing out of 

 portions of the body surface into projections known as pseudopodia — 

 usually with blunt rounded ends."^ The pseudopodia are pushed out 

 from any part of the surface indifferently and their tips end freely, never 

 fusing with one another. 



If a single pseudopodium is carefully watched during its protrusion 

 it is seen that its centre is occupied by an outwardly rushing stream of 

 endoplasm. The ectoplasm which bounds it may often be observed 

 not to reach quite to the tip — the extending tip being formed of granular 

 endoplasm. Such endoplasm, however, exposed on the surface of the 

 pseudopodium to contact with the water, is seen gradually to lose its 

 granular character and take on the appearance of ectoplasm. In some 

 kinds of Amoeba other than Amoeba proteus what are termed eruptive 

 lobopods are formed. When an eruptive lobopod is protruded what 



* Pseudopodia with blunt roimded ends are sometimes called lobopods to 

 distinguish them from other types of pseudopodia such as will be mentioned later. 



