ANIMAL CELLS 17 



in shallow dishes for several weeks, being careful not to allow all 

 the water to evaporate. Cultures of these materials should be 

 started in the spring for work in the autumn.) 



Mount on slides bits of the material from the different 

 dishes and search carefully for opalescent or transparent 

 spots that are constantly changing position. This is often 

 a little tedious, and needs to be persisted in to be success- 

 ful. 



Having found the animal, note its movements. Does 

 it always ntove in one direction ? Write a description of 

 the various movements of the amoeba. Judging from the 

 directions in which the amoeba moves, does it have an 

 anterior and posterior end? Of what is the body of the 

 amoeba composed ? Is the body clear or granular ? Find 

 an oval, transparent organ, the nucleus, within the body 

 mass. Is the amreba composed of one or more than one 

 cell ? Is the body inclosed by walls ? What, then, is the 

 great difference between this animal cell and the plant cells 

 already examined ? From what part of the body are the 

 streams of protoplasm sent out? Find the particles of 

 food surrounded by water. These are known as the food 

 vacuoles. How does an amoeba obtain its food ? See text, 

 page 15. How does it breathe? Note the contractile vac- 

 uole. This is a globule of clear liquid which forms near 

 the outside of the animal and discharges into the surround- 

 ing water. How often does it pulsate ? 



The contractile vacuole is an organ of excretion by which 

 the waste products are thrown out of the body. 



To see the nucleus in this animal and the following 

 one-celled forms, they should be killed by a one per cent 

 solution of acetic acid, when the nucleus will become visible 

 in the dead bodies. 



HERRICK LAB. EX. 2 



