AMOEBA 195 



the animal flows in that direction. When this happens the 

 ectosarc of the hinder portion of the body will be seen to 

 wrinkle as the entosarc flows away from it. 



Observe the granular nature of the entosarc and the flowing 

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

 protoplasm. Observe the food vacuoles in the entosarc ; they are 

 particles of food surrounded by water. Observe the pulsating 

 vacuole, the organ of excretion. It will be seen to be a large 

 globule of clear liquid which forms near the periphery and then 

 discharges into the surrounding water. Time its pulsations; 

 how many form a minute ? Add a 1 per cent, solution of acetic 

 acid to the water and find the nucleus. 



Exercise 2. Make a large semidiagrammatic drawing of an amoeba, 

 showing the features above mentioned, and label all. 



Amoeba has no special vegetative organs except the pulsat- 

 ing 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 move- 

 ments 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 opening in the ectosarc into the water. 

 Respiration is carried on through the surface of the body. One 

 reason for the active throwing out of pseudopodia is the neces- 

 sity 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 trans- 

 verse constriction 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 gradually lose their vitality and reproductive powers 



