700 ORDER: DIPLOMONADIDA 



towards the anterior centrosome, while the others pass to the posterior 

 centrosome. The chromosomes of each group then fuse to form a karyo- 

 some, and this is followed by constriction and division of the nuclear 

 membrane, so that two nuclei are formed. In the writer's experience, 

 G. intestinalis of man frequently shows nuclear pictures, which correspond 

 with all the stages figured by Boeck (1917) for G. microti, with the exception 

 of the actual division of the nuclei. In such preparations, though very 

 large numbers of flagellates are present, none of them is actually dividing 

 in the free stage. If the various nuclear appearances undoubtedly 

 represent a mitotic division of the nuclei, as first pointed out for G. intes- 

 tinalis by Rodenwaldt (1912), one would expect to find more frequently a 

 corresponding number of flagellates with two pairs of nuclei and others 

 with their bodies actually in process of fission. It is possible, as Roden- 

 waldt maintains, that usually the nuclei of the free forms prepare for a 

 division which is completed in the cyst. In one case noted above, the 

 writer and O'Connor (1917) encountered numbers of free flagellates actually 

 in process of binary fission (Fig. 292), and similar forms have been de- 

 scribed by Kofoid and Swezy (1922), so that it has to be admitted that 

 division in the free state can take place. 



Kofoid and Christiansen (1915, 1915cf) have described multinucleate 

 stages of G. ?nicroti and G. 7nuris. Both the free flagellates and. the 

 encysted forms are described as dividing by multiple segmentation. It 

 is remarkable that in some of the figures the two normal nuclei of the 

 free or encysted flagellates are in the position and possess the characters 

 they usually have, while the other supposed nuclei are smaller and have 

 a different appearance. It is difficult to understand how such a multi- 

 nucleate condition can have arisen if the two normal nuclei are still in 

 their usual situation, and are iinaltered in size and appearance. The 

 writer has seen very much vacuolated specimens of G. intestinalis having 

 at the centre of each vacuole a granule which might be mistaken for a 

 karyosome. It seems highly probable that it is structures such as these 

 which have been interpreted as nuclei. Similar multinucleate cysts of 

 G. intestinalis have been described by Kofoid and Swezy (1922). As many 

 as sixteen nuclei are said to be present. In no case was division of the 

 encysted form or daughter flagellates observed. Noc (1909a) gave an 

 illustrated description of what he considered to be multiple division of 

 G. intestinalis. It was supposed that after nuclear divisions a number of 

 minute flagellates were produced, but it is evident from his figures that 

 some of the forms depicted are not G. iyitestinalis, even if they are living 

 organisms. 



Various species of Giardia have been described from man and animals, 

 but the specific characters are in most cases very ill-defined. Simon (1922) 



