506 rnifcrsify of California Puhlicafions in Zoology [Vol. -20 



bodies often appear coineidently with the disappearance of the gly- 

 cogen mass, it seems likely that the latter may function in the forma- 

 tion of the former (Kofoid, 1923). These may be used up early in 

 the developmental process as is evidenced by the fact that many of the 

 four-nucleate, five-nucleate, and eight-nucleate cysts do not possess 

 chromatoidals (pi. 44, figs. 17-19) or they may persist to the eight- 

 nucleate stage (pi. 45, fig. 21). These chromatoidal bodies in the latter 

 stages have the form of ma.ssed bundles of splinter-like processes as is 

 shown by the irregular ends of the masses (figs. 24, 27). It is likely 

 that these massed chromatin bodies are formed by a union of the 

 smaller bodies that first appear around the margin of the glycogen 

 mass as is described for C. lafienri (Kofoid and Swezy, 1921). The 

 scattered aeicular and filamentous type of chromatoidal body so often 

 seen in E. coli has not been found in this species. 



Four-nucleate cysts may be found either with or without the glyco- 

 gen vacuole (pi. 44, figs. 16-17) though it is quite unusual to find the 

 vacuole persisting longer than to the four-nucleate stage. 



Nuclear phases. — As the nuclei within the cysts are frequently in 

 a state of mitotic change, it is necessary to regard these changes in 

 making a diagnosis. Nuclei in ej'sts, prior to the eight-nucleate stage, 

 may show figures representing any pha.se of mitotic development. The 

 typical resting nucleus is more often encountered in the eight-nucleate 

 cysts and on this account they are more commonly used as a basis of 

 diagnosis. 



The nuclear membrane of C. muris is characterized by its very 

 thin and transparent appearance. Small chromatin granules may lie 

 aroiuid the inner margin of the membrane, but this is common only 

 in the earlj- prophase. As a rule the nucleus is characteristically clear, 

 and in the middle is the dispersed karyosome (pi. 45, figs. 21, 24, 25). 

 Linin fibers connecting the karyosome with the nuclear membrane are 

 more common in the earlier than in the later divisions. The nuclear 

 membrane is so faint that it is frequently difficult to detect, and its 

 position can often be determined only by the limits of the cytoplasm 

 which surrounds the nucleus. This nucleus presents an entirely differ- 

 ent picture from the nucleus of E. coli, which has a thick membrane 

 heavily encrusted with chromatin granules, and from the nucleus of 

 C. decumani the more distinct membrane of which is usually encrusted 

 with several heavy chromatin blobs. 



The nuclei in the mononucleate cysts (pi. 43, fig. 7) are the largest, 

 and a corresponding diminution in the size of the nuclei is seen as the 



