182 SYSTEMATIC ZOOLOGY FOR TEACHER&. 



point lure to be emphasized is that neither ectoplasm nor entoplasm appear 

 to be separated, one grades completely into the other. 



Circulating System. Examined carefully, under a high power, amoeba 

 will be seen to possess, within its substance, a pulsating vesicle (see Fig. 

 66, B ) usually single, sometimes double, lying near its posterior extremity. 

 This is filled with a liquid which, upon a rather sudden contraction, of the 

 vesicle, is expelled. Then upon slow expansion, is refilled with the sur- 

 rounding protoplasm. By some observers this expelled protoplasm is said to break 

 tli rough the surrounding ectoplasm and escape into the water, and the vesicle 

 is regarded as excreatory. Others think that it creates a current in the inte- 

 rior of the animal, thus aiding in digestion. However this may be, the pul- 



Fig. 66. 



Amoeba, mucli enlarged. A, nucleus ; B, contracting vesicle ; C, pseudopodia ; D, food; E, food 

 balls. 



sating vesicle is clearly for circulating purposes, and must be regarded as the 

 direct homaalogue of the pulsating organ found in higher organisms, or in other 

 words, it is a rudimentary heart. 



Digestive System. A further careful examination of the amoeba, will 

 show small objects in its interior. These are often opaque and frequently 

 colored. These are food balls and enclose the material taken in by the 



amoeba. Bits of vegetable matter are taken in by being grasped by the 

 pseudopodia, and then the body flows around them completely enclosing 



