698 



ORDER: DIPLOMONADIDA 



numerous fibres which are difficult to trace. One pair of nuclei moves to 

 the opposite end of the cytoplasmic body, which divides longitudinally 

 to form two flagellates. There is no evidence that two flagellates ever 

 become encysted in a common cyst, as maintained by Schaudinn (1903), 

 Bohne and Prowazek (1908), and Woodcock (1915). Hartmann's (1909) 

 opinion that autogamy occurs in the cyst is likewise unsupported by fact. 

 In the smaller flagellates, which are probably the youngest forms seen 

 in any infection, each nucleus has a single central karyosome (Fig. 294). 

 In the larger or older individuals the karyosome is replaced by a 

 number of granules distributed upon a meshw^ork. It is supposed by some 

 observers that the formation of these granules is a preparation for nuclear 

 division, and that ultimately eight chromosomes are formed. Rodenwaldt 

 (1912) described the nuclear division of G. intestinalis . He noted that 

 the nucleus of the free flagellate contained either a central karyosome or 



Fig. 294. — Giardia intestinalis of Man, to illustrate the Growth of the Flagel- 

 late, FROM A Film in which dividing Forms were Present (x ca. 1,500). 

 (Original.) 



eight separate bodies. When a flagellate with a nucleus of the latter 

 type encysted, the eight masses or chromosomes arranged themselves in 

 two longitudinal rows, while the granules on the anterior end of the nuclear 

 membrane divided into two. The nucleus then became constricted at its 

 centre, and finally divided, each daughter nucleus receiving four of the 

 chromosomes. If this be correct, it would appear that the division of the 

 single karyosome in the flagellate stage into eight masses represents the 

 commencement of division, which is completed after encystment has 

 taken place. Kofoid and Christiansen (1915, 1915a.) described binary 

 fission of G. muris and G. microti, and Kofoid and Swezy (1922) that of 

 G. intestinalis. The process bears a close resemblance to that seen in 

 G. intestinalis by the writer and O'Connor (1917). The details of the 

 nuclear division were studied by Kofoid and Christiansen (1915, 1915a), 

 by Boeck (1917), and by Kofoid and Swezy (1922). The resting nucleus 

 possesses a central karyosome. The first stage in division is supposed to 

 be the division of the single pair of anterior blepharoplasts to produce 



