UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



Vol. 20, No. 8, pp. 199-234, plates 23-26, 1 1 figures in text March 7, 1922 



MITOSIS AND FISSION IN THE ACTIVE AND 

 ENCYSTED PHASES OP GIARDIA ENTERICA 

 (GRASSI) OP MAN, WITH A DISCUSSION OP 

 THE METHOD OP ORIGIN OP BILATERAL 

 SYMT^IETRY IN THE POLYMASTIGOTE 

 PLAGELLATES 



BY 



CHARLES A. KOFOID and OLIVE SWEZY 



CONTENTS 



Introduction 199 



Material and methods 201 



Morphology 202 



The active flagellate 202 



The neuromotor system and its relation to the symmetiy of the organism 205 



Mitosis in the active phase 212 



The plane of fission 215 



The origin of bilateral symmetry in the polymastigote flagellates 215 



The encysted phase 217 



Dedifferentiation in encystment , 22] 



Function of encystment 222 



Specific differences between GiardUi enterica and Giardia from rodents 222 



Summary 224 



Literature cited _ 225 



Explanation of plates 228 



INTRODUCTION 



Giardia eitt erica is a. flagellate para-sitic in the liiiman intestine, and 

 of general distribution throughout the world. It is widely prevalent 

 in the tropics, occurs rather frequently in our southern states (Stiles, 

 1915), and is found more often in children than in adults. It often 

 attends cases of acute or chronic diarrhea, achylia, duodenal ulcer, and 

 cancer of the stomach, though clinical evidence that it is an etiological 

 factor in these diseases is inadequate or lacking. 



