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GENERAL ZOOLOGY 



duction two trophozoites, also known as gametocytes, unite and 

 become encysted (pseudoconjugation) within a single envelope, 



Fig. 209. — A, Amoeba polypodia, dividing. (After Schulze.) B, Difflugia 

 urceolata, having a shell composed of grains of sand held together by chitin. 

 (After Leidy.) C, Actinospherium eichhorni, a multinucleated heliozoan without 

 a skeleton; the oblong objects in the medullary region are food particles; two 

 contractile vacuoles are shown in the cortex. (After Hertwig.) D, Acanthom- 

 etra elastica, a radiolarian with a spiny skeleton; the central capsule contains a 

 large number of small rounded nuclei. (After Hertwig.) (A, C, and D redrawn 

 from Hertwig, Manual of Zoology, by Kingsley, Henry Holt & Company.) 



the gametocyst. Each conjugant then forms gametes, those 

 from one individual uniting with those from the other to form 



