THE NUCLEI OF UROLEPTUS MOBILIS 331 



that in another, and certainly no theoretical interpretation of 

 the purpose of conjugation, admits a mortality of 100 per cent. 

 The explanation of such mortality must be sought in the environ- 

 mental conditions, and particularly in the culture medium used. 

 The continued life of Uroleptus ex-con jugants indicates a normal 

 condition of environment and a culture medium that satisfies all 

 conditions of vitality. 



The living ex-conjugants can be distinguished at a glance from 

 individuals in any other phase of vitality. They are shorter than 

 ordinary vegetative forms and larger in diameter. From dividing 

 forms, or individuals immediately after division, they are distin- 

 guished by the clear, non-refractile, vesicular macronucleus 

 which appears, vacuole-like, for two or three daj^s' after 

 conjugation. 



The young ex-conjugant contains, in addition to the new mac- 

 ronucleus and two new micronuclei, the granular remains of the 

 eight original macronuclei (fig. 86, one hour old). In some in- 

 dividuals, the typical linear arrangement of the original macro- 

 nuclei is retained (fig. 86). In others there is some confusion in 

 arrangement with a tendency to mass near the center (fig. 87). 

 In all cases such massing eventually occurs preliminary to final 

 absorption and always in the posterior half of the cell. During 

 the first forty-eight hours after separation, each of the eight 

 macronuclei which had developed increasingly large granules 

 during the conjugation stages again forms a compact, spherical, 

 homogeneous mass of chromatin which takes an intense nuclear 

 stain (fig. 87). These slowly disappear by absorption in the 

 protoplasm. First one, then another, loses its staining capacity 

 and fades awa}^ leaving no trace. In some cases, however, they 

 again undergo granular fragmentation before being absorbed in 

 the cytoplasm (figs. 88 and 89). Ultimately, four to five days 

 after separation, not a trace remains of the old macronuclei. 



In the meantime a new macronucleus is developing. The pale 

 ghost-like character of this cell organ is retained for at least 

 three days, but it becomes much larger and ellipsoidal in form 

 during this period (figs. 89 to 91). The granules within, and 

 solidly filling it, now assume a definite spherical form and begin 



