1924] 



Kessel : Amorbiic of Cidture Rats and Mice 



513 



matoidal bodies are not found as commonly in the cyst of C. decumani 

 as in those of C. muris. Chromophile ridges (pi. 48, fig. 51) are not 

 common in this species, traces of small ones having been found only 

 three times. 



The structure of the nuclei is the important feature differentiating 

 the cysts of C. decumani from those of C. muris. As already noted 

 in the motile forms, the nuclear membrane is more distinct in C. decu- 

 mani than in C. muris, and small granules or large blobs of chromatin 

 material are encrusted on the inner surface. This presence of char- 

 acteristic chromatin material on the nuclear membrane is a constant 

 feature throughout all the stages of mitosis. The typical resting 

 nucleus is characterized by the presence of an excentric karyosome 

 which is much more massed than the karyosome of C. muris (pi. 48, 



fig. 52), and yet, in certain instances, presents a tendency toward 

 diffusion (pi. 46, fig. 37). Linin fibers connect the karyosome and 

 nuclear membrane, and these can usually be ea.sily detected, even in 

 the eight-nucleate cysts. The nucleus, seldom, if ever, presents the 

 transparent appearance of the nuclei so characteristic of C. muris. 



The majority of the cysts are spherical, though ellipsoidal (pi. 46, 

 fig. 35). and irregularly-shaped forms (pi. 47, fig. 49) are found. The 

 irregular shape of the cyst in figure 49, simulates the shape of a motile 

 amoebae. One wonders if Schaudinn (1903) did not confuse irregu- 

 larly-shaped cysts of this type with motile amoebae when he elaborated 

 his theory of ' ' .schizogony ' ' for E. coli. 



As in C. muris, three races of amoebae have been determined in 

 ('. decumani, the .smallest averaging 14/i, the next 15.5/^ and the largest 

 17,u (see table 6). The eight-nucleate cyst is regarded as the typical 

 mature cyst, but instances of sixteen-nucleate cysts have been found 

 (pi. 48, fig. 52). In this case the cyst is abnormally large, being 22/^ 

 in diameter. 



