48 GARY N. CALKINS. 



developed cilia and regeneration had progressed to that extent 

 but no further (Fig. 2). 



The two cases of regeneration were 3 and 6, only one of which 

 was a vegetative form, the former being cut while dividing the 

 latter during a vegetative stage. Number 3 was first cut in the 

 plane of division separating the two cells; one of these was then 

 cut again in the first zone. On the following day both cells were 

 normal P. caudal um, but the cell that had been cut was much 

 smaller than the sister cell. The cut one died on the third day. 



The vegetative form that regenerated showed after 24 hours 

 an anterior end somewhat blunt but rounded and ciliated, and on 

 the following day it had divided twice, giving rise to four cells 

 which could not be distinguished from normal cells. The double 

 division indicates that the original cell was about ready to divide 

 at the time of cutting and that removal of the anterior part had 

 no effect on the subsequent divisions. 



Analysis of Table II. 



The mortality of Paramecium cut through zone 2 is consider- 

 ably greater than that for zone I. One chief reason for this is 

 probably the fact of the injury or destruction of the macronucleus 

 which usually occupies this region. Of the 68 cases 47.4 per 

 cent, died before the end of the first 24 hours; 79.4 per cent, were 

 dead before the end of 48 hours; but if the fragments lived 

 through this period there was a good chance of continued life 

 for some days, at 72 hours for example there were only 83.8 per 

 cent, dead, only a slight increase over the mortality at the end 

 of 48 hours. The majority of these or 8 out of 1 1 were monsters 

 while 3 out of the 68 regenerated into perfect cells. 



Of those that lived 48 hours or more after cutting, some (5) 

 failed to divide or else formed monsters; others divided in the 

 plane of the original center of the cell giving rise to (a) cells with 

 reduced vitality which soon died; (6) one normal cell and one 

 abnormal which died; (c) one normal cell and one abnormal 

 which divided more than once; (d) one normal and one ab- 

 normal cell which formed a monster, and (e) two normal cells. 



Of the four cases living 48 hours or more in which no division 

 occurred, tin- history was varied; the experiments were numbers 



