AMCEBA 129 



Amoeba. Continued formation of pseudopodia in one direc- 

 tion results in locomotion in a definite direction, but the move- 

 ment is seldom definite in Amoeba proteus. After any given 

 pseudopod has attained a certain size it ceases to extend, the 

 streaming of the granules in its interior becomes slower, and 

 eventually the flow is reversed. Another pseudopod has 

 been forming in some different direction, and the granular 

 " endoplasm " streams off into it, the older pseudopod 

 diminishing in size and finally becoming obsolete. 



These phenomena have led zoologists to describe a definite 

 division of the body of the Amceba into two parts, an outer 

 hyaline and firmer ectoplasm, and a more fluid endoplasm 

 containing granules and vacuoles, and also various foreign 

 substances which have been taken in as food. But recent 

 researches make it doubtful whether there is any permanent 

 differentiation of the cytoplasm into ectoplasm and endoplasm. 



In a large number, if not in all Amoebae, it may be shown 

 that the cytoplasm, the hyaline border as well as the granular 

 central part, has the structure of an exceedingly fine sponge- 

 work, or rather, let us say, a foam. Imagine a foam or froth 

 composed of bubbles of extremely minute size. Imagine that 

 the skins of these bubbles are composed of a somewhat denser 

 tenacious material and that their cavities are occupied, not by 

 air, but by a watery fluid. The bubbles in the centre of the 

 froth would be polygonal through mutual pressure ; and if the 

 whole thing could be hardened and cut into slices the sections 

 of the walls of the bubbles would look like a network having 

 somewhat irregular polygonal meshes. Such a foam may be 

 made by mixing up finely-pounded common salt with olive oil 

 which has been kept for a long time so as to be slightly rancid 

 and of a thick consistency like treacle. A small droplet of 

 this mixture, placed in water and examined under the micro- 

 scope, exhibits a structure which is marvellously like that of 

 the cytoplasm of an Amoeba. It is also divisible into an outer 

 more hyaline border and an inner granular mass, and it has 

 been shown that the outer hyaline border is due to the special 

 form assumed by the alveoli or bubbles in consequence of the 

 surface tension produced by the contact of two immiscible 

 liquids of different densities. A similar arrangement of the 

 alveoli is found in the so-called ectoplasm of the Amoeba, and 

 it is permissible to assume that the similar effects observed 



