ROBERT E. EAKIN 



401 



sands of organisms for the gross effects of a number of extrinsic 

 and intrinsic factors which affect development. For example, infor- 

 mation which we gained from later histological studies enables us 

 now to look at gross regeneration data and make some educated 

 guesses of interstitial cell patterns. Our ultimate goal is to relate 

 the effect of physiological and chemical agents to much more 

 specific phenomena — namely, changes induced in biochemical and 

 structural patterns during the regenerative process, such as those 

 described in the histological and enzymatic investigations I shall 

 mention presently. 



One intrinsic factor — the genetic differences in strains — is 

 illustrated in the left half of the first figure ( Table 1 ) which shows 

 the differences in the gross macroscopic responses that have been 

 studied in detail in seven strains of hydra (representing three 

 different species), the experimental procedures being those reported 

 in our previous publications ( 2, 3, 4) . 



Htjdra littoralis — Strain I: These were Hydra derived from the 

 clone initially used in this laboratory ( 1 ) and provisionally identified 



TABLE 1 

 Effect of site of severance upon rate of regeneration 



Each value represents the average of 36 repHcates. 



"Tentacle number at 48 hours. 



"" Length :widtli ratio of the longest tentacle. 



