1 1.4 MANUAL OF ELEMENTARY ZOOLOGY 



tractile vacuole adheres to the inner surface of the ectoplasm 

 and moves with it. The constant changes of position of 

 internal bodies is one of the arguments which support the 

 foam theory of the structure of protoplasm (see p. 85) 

 against theories which demand the existence in it of a 

 meshwork of fine threads, and an examination under high 

 powers of the microscope confirms this by revealing 

 appearances similar to those found in certain artificially made 

 foams. 1 This is especially noticeable in surfaces, such as 



-nzts. 



Fig. 70. — Part of an Amaba proteus, very highly magnified, 

 showing the foam-like appearance in the protoplasm, and 

 some of the granules which it contains. 



at., Regular layer of compartments in the cytoplasm around the nucleus ; 

 at., similar structures in the outer layer of the nucleus ; ec, ectoplasm ; 

 en., endoplasm ; nu. , nucleus. 



those where the cytoplasm and nucleus are in contact. 

 Each surface has a very regular row of minute bubbles 

 known as the alveolar layer. A similar layer is said to 

 exist in the ectoplasm, the outer walls of its bubbles 

 forming the surface, which behaves like an exceedingly 

 fine skin. This is known as the pellicle, and is believed 



1 Such a foam may be made by mixing together rancid oil and salt 

 and placing little droplets of the mixture in water. 



