6 E. J. LUND 



Dedifferentiation of an anterior or posterior half (figs. 11, 12, 

 13) before it again differentiates, is more complete than during 

 normal division (cf. figs. 13 and 4). The pieces assume a 

 spherical shape before differentiation takes place. Generally all 

 trace of the mouth and gullet disappears. It seemed to be true 

 that larger pieces, for example anterior or posterior two-thirds, 

 did not dedifferentiate as completely as the smaller pieces, for 

 usually in the larger pieces traces of the oral apparatus never 

 completely disappeared. 



A fully dedifferentiated piece may either encyst or differentiate 

 to a normal individual. Encystment often takes place after a 

 piece has differentiated and formed a normal individual, but in 

 every case dedifferentiation of the regenerated piece occurs 

 before encystment. The arrows between figures 13, 14, 15 and 7 

 indicate the possible sequence. These results are based upon 

 individual records of hundreds of cut pieces. Right and left 

 halves formed by cutting the individual lengthwise undergo 

 dedifferentiation and differentiation closely similar to anterior 

 and posterior halves. 



The nuclear apparatus consists of about 9 to 15 small micro- 

 nuclei (not shown) and one large macronucleus (mri). Pieces 

 without a part of the macronucleus never regenerate, but re- 

 generation is possible in pieces which contain only a small part 

 of the macronucleus. The size of the macronuclear piece included 

 seemed to have no effect on the rate of regeneration, for two 

 halves of an individual, one containing a small and the other a 

 very large piece of the macronucleus usually regenerated in 

 about the same length of time, — as shown by the records. All 

 pieces which regenerate, presumably have one or more micro- 

 nuclei. This point would be difficult to decide because of the 

 small size of the micronuclei in Bursaria. 



2. By mechanical injury without removal of parts of the cell 



If the anlage of the gullet of any dedifferentiated individual 

 is injured by tearing it with a needle and if the injury is not too 

 great the cell may continue to differentiate but the wound per- 

 sists as a more or less abnormal part of the gullet which other- 



