AMCEBA. 3 



a. Vacuoles are spaces filled with fluid, which is less 



dense than the surrounding protoplasm. They 

 contain in many cases foreign particles taken in 

 as food. 



b. The pulsating vacuole is a space filled with a 



watery fluid. It is fairly constant in pos-ition^ 

 and pulsates rhythmically. More than one may 

 be present. Twie its 'pulsations. 



c. The nucleus is a spherical or ovoid body, denser 



or more highly refractive than the rest of the 

 endosarc. During life it is not easily seen, but 

 it is rendered obvious by killing the animal with 

 acetic acid (1 per cent.), or by staining with 

 safranin. More than one may be present. 



C. Movements. 



The constant but slow change of form already referred 

 to is known as ' amoeboid movement.' Pseudopodia are 

 protruded from any point of the surface, and can be com- 

 pletely withdrawn, and a slow crawling movement of the 

 whole animal can be efi'ected by their means. Pseudopodia 

 may also surround particles of food and then be withdrawn, 

 bringing the food particles into the body. 



Draw a specimen of Amceha several times at intervals of 

 half a minute, indicating the direction of flow of the particles 

 by means of arrows. Compare the drawings, and note the 

 differences of form even in sluggish specimens in which move- 

 ment was not obvious. 



Feed with indigo or carmine, or other finely divided 

 pigment, and note that food is taken in at almost all parts of 

 the surface. 



D. Keproduction. 



Amceba multiplies by fission ; that is, the whole mass 

 divides into two, each containing a portion of the nucleus, of 

 the endosarc, and of the ectosarc of the original cell. 



b2 



