AXIAL GRADIENT IN CILIATE INFUSORIA. 45 



majority of cases with the appearance of a rounded swelling over 

 the anterior vacuole. The ectoplasm involved loses its cilia 

 and its characteristic structure but a thin membrane remains 

 surrounding the swelling. The swelling gradually increases in 

 size and becomes a spherical mass into which the anterior vacuole 

 often passes (Fig. 15). Here the vacuole undergoes enlargement 

 and does not contract rhythmically but finally disappears. The 

 vacuole is surrounded by granular cytoplasm. In other cases 

 the anterior vacuole remains in its normal position and the 

 swelling contains only granular cytoplasm (Fig. 16). In all 

 cases the swelling is lighter in color than other parts of the body 

 and the characteristic structure and the cilia of the region have 

 disappeared. 



Occasionally the swelling appears over the posterior instead of 

 the anterior vacuole (Fig. 17) but this is comparatively a rare 

 occurrence. In a few individuals among the thousands observed 

 swellings of about equal size appeared over both vacuoles (Fig. 

 1 8) and in a few other cases a larger swelling over the anterior, 

 a smaller over the posterior vacuole. But in at least nine out of 

 ten the swelling appeared only on the anterior vacuole. 



The swelling gradually enlarges, while the animal continues to 

 swim, the vacuole disappears sooner or later (Fig. 19) and the 

 intact portion of the body gradually decreases in size, the ecto- 

 plasm evidently undergoing contraction as the entoplasm gradu- 

 ally passes into the swelling (Fig. 20). At this stage the animal 

 is still swimming, the structure of the ectoplasmic regions not 

 involved in the swelling is intact and meganucleus and posterior 

 vacuole retain their positions. As noted above the cytoplasm 

 in the swelling, which is now as large as the remainder of the 

 body, is lighter in color and more transparent and more uniform 

 in appearance than in the intact regions. It is evidently dead 

 and some of its constituents have probably diffused through the 

 membrane as does the blue pigment in the case of Stentor. 



The disintegrative change gradually spreads over the ectoplasm, 

 less rapidly on the side of the oral groove than on the opposite side, 

 and the intact ectoplasm continues to decrease in size (Fig. 21). 

 The cilia on the intact portion are still present and beating at this 

 stage and the animal may move slowly in a circular course with 



