104 



GARY N. CALKINS 



was complete regeneration of the micronucleus-holding fragment, 

 while the other fragment failed to regenerate. Experiment 34 

 is a typical case of this group. Here the cell was cut almost 

 through the center as shown in fig. 7. The anterior part (A), 

 without a micronucleus, did not regenerate and was killed after 

 72 hours (see fig. 7 A) ; the posterior part (B) regenerated perfectly 

 in 24 hours. 



B 



8 ^ 



Fig. 8 Experiment 21. Cell from 24 to 30 hours old. Both fragments regener- 

 ated perfectly in 24 hours, although A was one-quarter size. 



Fig. 9 Experiment 37. Cell from 6 to 8 hours old. Both fragments regenerated 

 in 24 hours. B, however, did not grow but died the following day. 



Experiments 21 and 37. Here the cells were cut as above but 

 both fragments in each case regenerated into perfect organisms. 

 In no. 21 the cell was 24 hours old when cut through the center as 

 shown in fig. 8; after one hour A showed no sign of regeneration 

 but B had replaced 4 membranelles ; after 2 hours A was still not 

 regenerating, but B had 6 membranelles. Finally, after 24 hours, 

 A was completely regenerated but only of one-quarter size, while 

 B was full size and normal. After 48 hours both were large and 



