AMOEBA PROTEUS 45 



changing, the structure remains practically the same. It is 

 always one protoplasmic unit, a cell and like other cells it is 

 differentiated into cell body, called cytoplasm, and nucleus. 

 This nucleus is composed of slightly different protoplasm from 

 that of the cell body chiefly characterized by the greater affinity 

 for basic stains, while the protoplasm of the cell body has an 

 equivalent affinity for acid stains. The substance of the nucleus 

 which takes the stain is called chromatin and is composed chiefly 

 of nucleins or nucleo-proteids particularly rich in phosphorus. 

 The nucleus can be seen in life as a pale circular disc moving 

 with the flow of granules from one part of the cell to another 

 and turning as it moves showing now the circular outline, 

 again the flattened edge view. 



Endo plasm and Ectoplasm. The cytoplasm is not entirely 

 homogeneous but is differentiated into an inner and an outer 

 portion. The former, in which the nucleus is found is called 

 the endoplasm, or sometimes, the endosarc. The latter, called 

 the ectoplasm, although soft and gelatinous, is firmer and denser 

 than the endoplasm and is more transparent for it has none of 

 the refractive bodies found in the endoplasm. It is to be re- 

 garded as a protective layer, it being the part that comes in 

 contact with the surrounding medium and through it all inter- 

 course between the amoeba and the environment must take 

 place. In other forms of protozoa it is this ectoplasm which 

 becomes differentiated in the greatest variety of ways for pur- 

 poses of protection, locomotion, and sensation. 



The endoplasm, on the other hand, contains the vital organs 

 of the cell, a number of which can be seen with little effort. 

 Large particles more or less disintegrated, and surrounded by 

 clear fluid, are food bodies recently ingested and are undergoing 

 digestion in the fluid-filled spaces, which, for this reason, are 

 called gastric vacuoles. The bodies in these vacuoles may fre- 

 quently be recognized as portions of other minute animals or 

 plants. Another fluid-filled sphere usually best seen near the 

 periphery of the cell, is perfectly clear and without solid particles 

 of any kind. It suddenly disappears, the contained fluid being 

 excreted to the outside through the ectoplasmic layer. It 



