ZooL.— Vol. III.] STEVENS— CILIATE INFUSORIA. 27 



Figures 61-66 show sections of stages corresponding to 

 those shown in figures 39-44, in which may be compared 

 the changes in the chromatin granules as far as made 

 out. The minute structure of the macronucleus of Boveria 

 is a difficult object of study, especially in these stages of 

 division, and many points remain unsettled, which it is 

 hoped that further studies and experimentation with fixing 

 fluids of varied composition and strength may clear up. 

 Chief among these is the detail of the division and distri- 

 bution of the chromatin granules so clearly seen in figs. 



41-43- 



Comparison of the figures just cited shows that while 

 subject to considerable variation there is a decided tendency 

 in the micronuclei to take positions at the poles of the mac- 

 ronucleus during division. Division of the micronucleus 

 and polar migration of its halves invariably precede division 

 of the macronucleus. No specialized morphological con- 

 nection, however, has been made out between micronucleus 

 and macronucleus at any stage ; so that for the present, at 

 least, their reciprocal positions must be regarded as merely 

 coincident phases of the same general physiological process 

 of division, though one is strongly tempted to consider the 

 bearing which these phenomena may have upon the phylog- 

 eny of the centrosome. 



Though division in Bovei'ia, when observed superficially, 

 appears to be a process of budding, careful examination of 

 the details shows that we have here, not ordinary budding 

 as in S^irochona^ where the daughter animal is wholly a new 

 growth and separates from the parent in an immature state, 

 but what may be styled oblique fission. It will be observed 

 from comparison of figs. 37-46 that one individual, — the 

 right-hand one in fig. 44, — receives the peristomal half of 

 the parent animal, its aboral portion being newly formed, 

 while the other individual has a newly differentiated peris- 

 tomal region joined to the aboral half of the parent animal. 

 Figure 39 shows well the division of the original animal 

 between the two daughter animals. 



