118 University of California Publications in Zoology [Vol.20 



York, N. Y., from December 28, 1918, to May 30, 1919, on 3301 stools 

 from 2300 men who had been overseas, mainly in France, and from 

 576 men, chiefly of the medical detachments and food handlers, who 

 had seen only home service. In the former group there were 97 

 persons infected or 4.2 per cent, and in the latter 20, or 3.5 per cent. 

 At Berkeley 1836 stools of 534 persons have been examined, with 

 28 cases or 5.3 per cent of infection. 



Although a common and widely distributed parasite of man, 

 this organism has often been regarded as a tropical form. It has 

 undoubtedly been confused, in much of the clinical literature, with 

 other intestinal flagellates, especially with Trichomonas, and its 

 structure, relationships, and encysted stages have been imperfectly 

 described and figured and sometimes even misinterpreted as those of 

 another flagellate. Conclusions as to its pathogenicitj' are also at 

 variance. 



The data here presented add to our knowledge of its wide dis- 

 tribution, and give, for the first time, a full analysis of its finer 

 structure, especially of its neuromotor apparatus and of its mitosis 

 in the encj'sted stage. This aifords a satisfactory basis for conclusions 

 as to its systematic relationships, a suggestion as to the holdfast func- 

 tion of the cytostome, and a critical basis for the accurate detection 

 of this genus and its differentiation from the other parasites with 

 which it is associated in the intestine of man and other mammals. 



We present a full analysis of the structure of Chilomastix, 

 especially of the neuromotor system, and by the homology of its 

 elements find that Chilomastix is closely related to Giardia, and is a 

 transition form from the monozoie to the diplozoic polymastigote 

 flagellates. 



Our analysis has added the following organs to those hitherto 

 detected : the centrosome, nuclear rhizoplast, peristomal rhizoplast, 

 peristomal fiber, paradesmose, and the spiral groove (as a pennanent 

 organ). "We have also detected and analyzed intracystic mitosis. 

 Our interpretations of the precise relations of the flagella to the 

 blepharoplasts and of the organs of the cytostomal rim, which we 

 designate as parastyle and parabasal, differ from those of previous 

 writers and make possible a fuller comparison of Chilonmstix and 

 Giardia, and establish intimate relationships between the two genera. 



