112 GARY N. CALKINS 



90 hours B was dead without regenerating. This experiment is 

 interesting because the central and largest piece not only failed 

 to divide through the original plane of division, but also failed 

 to regenerate. 



Experiment 30 was in connection with a cell in the early phase of 

 division. The first cut was through the posterior part of the 

 macronucleus, the second was longitudinally through the anterior 

 fragment. After 18 hours A' was complete and normal. A" was 

 not regenerated while B was complete but with a large cirrus 

 arising from the middle of the adoral zone. After 42 hours both 

 A' and A" were complete and normal while B remained as before. 

 In no. 40 a form in the mid phase of division, all three parts were 

 alive but nat regenerated after 24 hours. The next day two of 

 the three were dead and the third not regenerated, and this too, 

 died before the end of the 73d hour. 



Similar results were obtained with other forms cut two or more 

 times, the larger pieces of dividing forms regenerated, the smaller 

 ones not, and in some cases no regeneration occurred. 



GENERAL 



These experiments indicate that in Uronychia the power of 

 regeneration is greatest at the time of division. They indicate, 

 furthermore, that something is present in the cell body at this 

 period which is not present at other times. The organism, if cut 

 immediately after division has a very limited power of regenera- 

 tion, and then only when both parts of the nuclear apparatus are 

 present. In some cases even when the cell is provided with all of 

 the cellular organs, as in experiment 42 (fig. 4A, p. 101), regenera- 

 tion failed; or again, as in no. 43 where a portion only was removed 

 from the peristomial region, the cell failed completely to respond. 

 Fig. 3B shows that the nucleus is still condensed immediately 

 after division, after a couple of hours, however, the characteristic 

 form of the resting nucleus is assumed and growth has begun, 

 while after from six to twelve hours th-^ cell is full-sized and nor- 

 mal. Even at this period however, the power to regenerate is 

 very limited as shown in section 3. Here, out of ten cases in 

 which both parts were retained, only two resulted in complete 



