52 (,ARV N. CALKINS. 



Of the vegetative forms the most interesting cases were nos. 

 7 and 19, the former typical of the majority of cases, the latter 

 unusual. No. 7 was a small form cut just below the mouth. 

 It grew very large but did not regenerate nor divide in the four 

 days of observation, and was finally killed. The nucleus \\a-- 

 normal although main- fragments of macronuclear material in- 

 dicated that the original cell was a recent ex-con jugant and was 

 in about the fourth generation when cut. 



No. 19 was more interesting. It was cut just below the mouth 

 as in the preceding case. In 24 hours it had grown very large 

 and had divided through the original center of the cell, forming 

 one normal and one truncated cell (Fig. 9, Plate I.). The normal 

 cell divided again before the third day forming two perfectly 

 normal paramecia which were then discarded. The truncated 

 cell grew very large before the third day and divided on the 

 fourth day into one small abnormal cell (Fig. 9, b, c, e) and one 

 larger normal cell (Fig. 9, d}. On the fifth clay the larger, 

 normal form had divided while the small truncated one had 

 developed a sharp posterior end and was almost normal in appear- 

 ance; finally on the tenth day, all were living and all normal save 

 for a noticeable difference in size (Fig. 9, g, Ji, -i, j). Here, thi 

 fore, there was a gradual return, through four or more generations 

 to the normal form, although the single cell failed to regenerate. 



Analysis of Table IV. 



Cells cut in the extreme posterior end were seriously damaged 

 although the abnormalities were not so marked as in the other 

 experiments and 10 per cent, of them regenerated. Only 40 

 per cent, were alive after 24 hours and only 20 per cent, after 

 48 hours showing that, although not much mutilated, vitality 

 was nevertheless badly affected by the operation. There were 

 no monsters, although in one case (no. 7) the cell divided 24 

 hours after cutting but the daughter cells had great difficulty 

 in separating, remaining attached by a narrow isthmus of proto- 

 plasm for one full clay and finally separating. Within a tew 

 hours after separation, however, both cell- died. This remarkable 

 effect was produced by cutting off only the most posterior tip 

 of the original cell. It seems hanIK credible that so marked an 



