1!)24| Ke-ssel: Amoebae of Culture Rots and Mke 507 



number of iniclei increases. For a ratio of the size of the nuclei in this 

 species and in C. decumani see Kofoid, Swezy, and Kessel (1923a). 

 In material obtained after the administration of a purgative and 

 from autopsies, the eight-nucleate cysts are the most numerous while 

 the binueleate cysts are next in number. The binucleate cysts usually 

 show some form of mitotic spindle and it is from this type of cyst 

 that the majority of the chromosome counts have been made. 



No sixteen-nucleate cysts have been found from this species, though 

 nuclei have been found in the eight-nucleate cysts which indicate that 

 a further division is in progress. 



Chromophile ridge. — In a majority of the eight-nucleate cysts, a 

 dark-staining ridge is found, which is located in the cytoplasm along 

 the inner margin of the cj'st wall. It maj' often extend a distance 

 ranging from one-quarter to one-half of the circumference of the cyst 

 (pi. 45, figs. 20, 25). This ridge is not to be confused with the chro- 

 matoidal bodies, which are usualh' not curved and as a rule lie 

 embedded in the cytoplasm. Similar ridges, which they have termed 

 chromophile ridges, have previously been described in Councilmanki 

 lafleuri by Kofoid and Swezy (1921). It is significant to note that 

 Wenyon (1907, pi. 10, fig. 1) has figured a cyst which presents this 

 typical structure. 



Budding 



Although it is a fact that the motile amoebae divide by simple 

 fission, it is to be noted that this process is comparatively rare, few 

 mitotic spindles ever having been recorded in motile forms and only 

 a few instances of binucleate motile forms ever having been seen. 

 The present investigation verifies this rarity of dividing motile forms, 

 even in material collected from the caecum of autopsied animals. How- 

 ever, in these same caeca numerous cysts have been found, a fact which 

 indicates that multiplication by encystment in this species of amoeba 

 may be much more common than multiplication by binarv fission of the 

 motile phase. 



The determination of the manner by which the amoebae escape 

 from the cysts has presented numerous difficulties and has called forth 

 several interesting theories. In E. dysenterim it is generally thought 

 that in some manner the four-nucleate amoeba escapes from the cyst, 

 and that subsequent division into four amoebulae occurs (Chatton, 

 1917; Dobell and O'Connor, 1921). Again, E. coli is supposed to 

 escape from the cyst in a similar manner as an eight-nucleate amoeba 



