20 MANUAL OF ANIMAL BIOLOGY 



parent liquid. It slowly flows in various directions, depending 

 largely upon the environment. This movement results in the 

 formation of irregularly shaped, protoplasmic projections, known 

 as pseudopodia. 1 It is by means of the flowing movement, with 

 the consequent formation of pseudopodia, that the animal moves. 

 A movement of this type, as has been previously noted (B. p. 16), 

 is known as amoeboid movement. The exact nature of amoeboid 

 movement is not fully established, even though it has been the 

 subject of a large amount of research work. (B. f. 1 : W. fs. 6, 13.) 



The endoplasm, in comparison with the ectoplasm, is not so 

 viscid a substance and it has a tendency to flow more readily. 

 Observations on living Amoebae show, however, that in the forma- 

 tion of pseudopodia the flowing movement appears first in the 

 ectoplasm, and later the endoplasm rapidly streams into the ecto- 

 plasmic region where the pseudopodium is being formed. The 

 endoplasm is less transparent than the ectoplasm, and a micro- 

 scopic study with the proper type of illumination shows clearly 

 that it is not a homogeneous material. It is generally believed 

 that the endoplasm consists of a basic ground substance in which 

 innumerable, ultramicroscopic particles are suspended. In addi- 

 tion to these particles, which apparently form a fundamental con- 

 stituent of the endoplasm, it will be found that there are also 

 many particles of various kinds, shapes, and sizes present which 

 are sufficiently large to be easily observed under the microscope. 

 For the most part these are transient, non-living, metaplasmic 

 materials, such as undigested particles of food, indigestible refuse, 

 etc., which have not been expelled. 



The endoplasm contains a number of other structures, the most 

 important being the nucleus, which is an essential part of every 

 cell. It is probably the directing center for all the life processes. 

 There is also a single contractile vacuole which collects and 

 expels the liquid and, possibly, gaseous wastes resulting from the 

 breaking down of living material, as well as the excess water taken 

 in with food. Numerous gastric vacuoles are present in which 

 the particles of food that have been taken into the animal are 

 being digested. The gastric vacuoles are temporary structures; 

 the number present in an Amoeba at any time depending upon 

 the amount of food material which is undergoing digestion. 



1 Singular, pseudopodium. 



