418 THE BIOLOGY OF HYDRA : 1961 



desmonemes were present. Although it was not possible to observe 

 migration of the immature interstitial cells, their presence in such 

 large numbers indicated that they had migrated. On the other hand, 

 there was no such accumulation of desmoneme-containing cnido- 

 blasts; hence, there could have been no significant amount of 

 migration of these cells. 



CELL MITOSIS 



Cell mitosis during regeneration was studied by early investi- 

 gators, many of whom did not regard this process as being im- 

 mediately essential for tentacle formation. Rowley (10), while 

 studying C. vindissima, concluded that the new cells are not formed 

 at the cut surface alone and that the tentacles do not seem to 

 be regenerated solely from new tissue. She felt that the new cells 

 which appear during the regeneration of hydra are formed by 

 division of the old cells throughout "the entire piece" (as in the 

 normally growing animal) and that the tentacles are formed from 

 old cells and from cells that have arisen by division of the already 

 differentiated cells of the old part. 



Except for a slight increase in mitosis noted by Ham and Eakin 

 (5), reaching a maximum at 45 minutes near the site of the cut 

 (a reaction possibly associated with wound healing), we have not 

 observed any increase in mitotic activity during the remaining 

 regeneration period. It is believed, therefore, that mitotic activity 

 if diffuse throughout the body of the hydra and there is no increase 

 in activity during normal regeneration or in hydra treated with 

 lipoic acid. The presence of all stages of mitotic activity in lipoic 

 acid treated hydra indicated that this process had not been altered 

 by exposure to this disulfide. 



Since interstitial cells are believed to be replaced through mitosis, 

 there most likely is an increase in this activity after the regeneration 

 period in order to replace those cells which differentiated into 

 the necessary components of the new tentacles. Further research, 

 however, will be necessary to determine the extent to which this 

 occurs. 



