1922] Kofoid-Sivczy: Mitosis and Fission in Giardia enterica 211 



mitosis. Typically they have the form above described, but in some 

 aspects, unless carefully focused out, they appear as a single mass. 

 For this reason, and also because in a moribund state degenerative 

 phenomena affect these organs, they have been figured as a single 

 median structure, a misleading and certainly atypical condition. Thus 

 Benson's (1908, fig. 2, see also Doflein, 1916, fig. 642&) figure of 

 Lamblia intestinalis from man has a single stout clavate parabasal 

 which probably is only the superposed members of the pair of para- 

 basals. The same type of parabasal appears in Hegner and Cort (1921, 

 pi. 4, fig. 6) in Simon's figure of Giardiu intestinalis from man. The 

 single parabasal appears in Grassi's (1883, pi. 3, figs. 3, 4) original 

 figures of Megastoma entericum (host not stated but presumably man) 

 and in those of Grassi and Schewiakoff (1888, pi. 15, fig.8) of Mega- 

 stoma entericum from rodents as well as in some of Metzner's (1901, 

 pi. 15) figures of Megastoma entericum from the rabbit. From the 

 nature of the figures it appears that failure to focus out and analyze 

 the pair of parallel parabasals underlies the interpretation or figure 

 of these organs as a single rather than a paired structure. We find 

 it possible to analyze the seemingly single bodies into the pair in our 

 material as a general rule and regard the other interpretations as 

 erroneous. 



The peristomal fiber {ant. and post, perist. /., fig. B) is a deeply 

 staining thread encircling the so-called cytostome of Giardia. It lies in 

 the immediate periphery of the concave depression on the anteroventral 

 surface of the body. Its anterior half has an almost semicircular 

 course, while posteriorly it has a recessed reniform one, the lateral ares 

 incurving anteriorly to the median line, along the inner ends of the 

 posterolateral flagella. The incurved arcs appear to fuse with anterior 

 sections of the axostyles as the latter curve dorsally over the recessed 

 cytostome. Along the inner edge of the anterolateral portiozi runs the 

 intracytoplasmic section of the anterolateral flagellum closely parallel to 

 and often obscured by it. The two are often drawn as a single fiber, as 

 in the figures of Prowazek and Werner (1914) and of Simon in Hegner 

 and Cort (1921). At the point where the flagellum crosses over the 

 peristomal fiber to emerge from the cytoplasm, often slightly posterior 

 to the middle of the lateral arc, there is generally a slight angle in the 

 otherwise regular curvature of the arc, but we have found no granule 

 there, as in Giardia microti and G. muris (Kofoid and Christiansen, 

 1915), though one appears in Simon's figure. 



