DOROTHY B. SPANGENBERG 421 



RETARDED INTERSTITIAL CELL DIFFERENTIATION 

 WITH NORMAL MESOGLOEAL RESTORATION 



111 normal regeneration, this relationship could account for 

 variation in the regenerative ability of normal hydra. It has been 

 demonstrated that the normal reserve of partially differentiated 

 interstitial cells varies in different strains of hydra (11). The time 

 required for the acquisition of the necessary number of differentiat- 

 ed interstitial cells is dependent upon the quantity of reserve differ- 

 entiated cells already available. Variation in amount of such re- 

 serves and in the rate of differentiation producing new ones could 

 account for \'ariation in normal regenerative ability of hydra pro- 

 vided the mesogloeal material is restored in all hydra at the 

 same rate. 



In lipoic acid "inhibited regeneration" {H. littoralis), the dif- 

 ferentiation of interstitial cells is definitely retarded, yet the meso- 

 gloeal material is restored at a normal rate. Once the mesogloeal 

 material is restored, it appears that the interstitial cells do not 

 differentiate sufficiently for regeneration to occur. However, if the 

 non-regenerated tip (and consequently the mesogloeal layer) is 

 removed several days hence (after cellular damage has been re- 

 paired) normal regeneration occurs. 



RETARDED INTERSTITIAL CELL DIFFERENTIATION 

 WITH RETARDED MESOGLOEAL RESTORATION 



This condition is observed in lipoic acid treated Chlorohydra 

 where the inhibitory effect expresses itself in one of two ways — 

 (a) either permanent inhibition (as in H. littoralis) or (b) 

 retardation with subsequent "wild" growth ( 13 ) . In case ( a ) , the 

 restoration of the mesogloeal mechanism may occur before suffi- 

 cient interstitial cell differentiation has occurred (as in lipoic acid 

 treated H. littoralis), and tlie hydra would be permanently in- 

 hibited. In case (b), the restoration of the interstitial cell differ- 

 entiation may occur prior to the restoration of the mesogloea, 

 resulting in the differentiation of more interstitial cells than nor- 

 mally occurs, and the hydra exhibit the "wild" growths observed. 



