416 THE BIOLOGY OF HYDRA : 1961 



Histological studies of lipoic acid treated hydra {H. littoralis 

 and Chlorohydra mridissima) revealed that, at 20 hours after 

 cutting, many undifferentiated interstitial cells were in the pre- 

 tentacle area, whereas only a few late-stage interstitial cells and 

 cnidoblasts containing desmonemes were present. This indicates 

 that normal differentiation of interstitial cells does not take place 

 in these hydra. Morphologically, however, the interstitial cells 

 appear normal as compared to controls. It is questionable, there- 

 fore, whether the differentiation of the interstitial cells is inhibited 

 by a direct action of lipoic acid on these cells or whether it is in- 

 fluenced by damage to another cell type which may normally 

 contribute some substance to interstitial cell differentiation. Histo- 

 logical sections of lipoic acid treated H. littoralis and C. mridissima 

 reveal that some of the gastrodermal cells are damaged. Whether 

 or not this damage of gastrodermal cells is related to reduced 

 interstitial cell differentiation in the epidermis is still to be deter- 

 mined. It is believed that many factors which influence the re- 

 generative process do so by interfering with interstitial cell differ- 

 entiation. 



CELL MIGRATION 



The importance of cell migration in morphogenesis has been 

 emphasized both in embryonic development ( 16 ) and in the re- 

 generative process ( 15) . 



Grafting segments of Chlorohydra from a normal clone (con- 

 taining green algae in their gastrodermal cells) to segments of a 

 modified clone ( no visible green algae ) revealed that during normal 

 regeneration gastrodennal cells migrate from closely adjacent re- 

 gions to participate in the regenerative reconstruction. Migration 

 of gastrodermal cells was not impaired in lipoic acid treated Chloro- 

 hydra, and in fact, the extent of cell migration appeared to be 

 increased (Fig. 1). It is possible that the increased migration 

 of gastrodermal cells following lipoic acid treatment results from 

 the need for replacement of the gastrodermal cells that are damaged 

 by the chemical ( 13 ) . 



On the basis of many observations made of regeneration of 



