202 University of California PiMications in Zoology [Vol. 20 



The material has been studied in fresh smears, in iodine-eosin 

 preparations, and mainly in iron haematoxylin stain following hot 

 Schaudinn's fluid (with 4 per cent acetic acid) as a fixer of smears upon 

 slides, by both the slow and rapid methods of staining. Strong illumi- 

 nation (100 watt Mazda) and Wratten filters Kl and G and immersion 

 oil between condenser and slide have been used in determination of the 

 fibrillar system by the monobjective binocular microscope. 



MORPHOLOGY 



The fact that the investigation of Giardia eiderica is, as a rule, 

 dependent upon stools rather than flagellates in place in the intestine 

 of the host, as in the ease of Giardia in mice, puts limitations upon 

 the amount and quality of material of the free flagellates available 

 for investigation. The free flagellates are rare in the faeces except 

 occasionally in diarrheic stools, and the moribund condition of many 

 of them usually limits the material available for critical study of 

 mitosis. It is quite otherwise in the cysts of this parasite, which find 

 their normal conditions of life in the discharged faeces. 



The Active Flagellate 



The shape of the body is remarkably uniform in properly fixed 

 material and is siibject to but slight modifications as a result mainly 

 of the varying degrees of contraction of the cytostome (cf. figs. 4 and 

 5, pi. 23, and fig. 6, pi. 24), and of the tail which may be more or less 

 elevated (fig. D; pi. 23, figs. 3, 5) or laterally deflected (pi. 24. fig. 8). 

 The constriction of the cytostome elevates the dorsal surface, and' the 

 tail may be elevated as much as forty-five to ninety degrees (Zabel, 

 1901) above the horizontal plane when the flagellate is in place on an 

 epithelial cell of its host. In the faecal smears the tail usually lies 

 horizontally in the plane of the peristomal region. 



The body is pyriform in outline in dorsal or ventral view (fig. B), 

 is flattened ventrally by the shallow, sucker-like cytostome, and is 

 contracted posteriorly into the tapering tail. In lateral view, it is 

 convex dorsally and flat ventrally, with the greatest elevation at the 

 level of the posterior margin of the cytostome (pi. 23, fig. 2). The 

 greatest transverse diameter of the body is at the level of the posterior 

 third of the cytostome and slightly exceeds (0.51-0.54) half the length. 

 The dorsoventral diameter is a little less than half the transdiameter 

 in stained and presumably contracted material, but appears to be 



