AMCEBA 159 



the granules as they move about with the motion of the proto- 

 plasm. Observe the food vacuoles in the entosarc ; they are par- 

 ticles of food surrounded by water. Observe the pulsating vacuole, 

 the organ of excretion, which is usually near the hinder end of the 

 moving body. It will be seen to be a large globule of clear liquid 

 which forms near the periphery and then discharges into the sur- 

 rounding water. Time its pulsations ; how many form a minute ? 

 Add a I per cent solution of acetic acid to the water, or a few 

 drops of aceto-carmine solution, and find the nucleus. 



Exercise 2. Make a large semidiagrammatic drawing of an amoeba 

 showing the features mentioned above, and label all. 



Amoeba has no special vegetative organs except the pulsating 

 vacuole. Solid food consisting of plants and animals and particles 

 of organic matter is ingested in the form of food vacuoles. These 

 move about in the entosarc with the movements of the animal's 

 body and the nutritive matters are digested and absorbed. Waste 

 matters are then egested by being thrust out of a temporary open- 

 ing in the ectosarc into the water. Respiration is carried on 

 through the surface of the body. One reason for the active throw- 

 ing out of pseudopodia is the necessity of increasing the relative 

 area of the surface of the body for respiratory purposes. 



Reproduction in Amoeba is carried on by division. The nucleus 

 first divides; the animal then elongates, and a transverse con- 

 striction appears in its middle, which is finally carried through 

 the body. Two animals are thus formed, each of which contains 

 half of the nucleus. As in other protozoans, reproduction in 

 Amoeba is largely dependent upon nutrition. If the nutritive 

 conditions surrounding them are unfavorable, the animals grad- 

 ually lose their vitality and reproductive powers and in the course 

 of time will die. Conjugation also probably occurs, as in other 

 Protozoa, although it has never been observed. 



