294 



distal rings is found frequently broken off. So, too, I have not in- 

 frequently seen regeneration occurring in nature from the unsegraented 

 tract. I do not, however, recall one indubitable case of regeneration 

 in nature from the proximal segmented tract. 



I am, therefore, led to conclude, that, while in Obelia, as in most 

 other animals, the capacity of any part for regeneration seems to be 

 a function of the frequency of the demand for regeneration, — of the 

 liability of the part to be called upon in the future to regenerate and 

 the frequency with which it has (in the race) been called upon in the 

 past, — we have in Obelia the additional fact that the definiteness 

 of regeneration of any part, its resemblance indeed to what has been 

 lost, is a function of the same factors. 



The fact of the relation between definiteness of result and require- 

 ments or experience seems to indicate the existence of internal ten- 

 dencies in the regenerative tissue of the distal end of the stalk, 

 directive tendencies not possessed by the proximal regenerative tissue, 

 whose development is therefore very indefinite. In the possession of 

 such (hypothetical) directive tendencies, the distal end may be said to 

 be more differentiated than the proximal. 



Allowing, however, for the greater definiteness of the result 

 in the more distal cuts, the curves of regeneration show no important 

 indication of difference in the germ-plasma at different 

 levels in respect to the size or form of the part which 

 regenerate. 



Third. The curves of regeneration bring out a second, wholly 

 unsuspected series of facts; namely, the tendency of the regenerative 

 tissue at all levels to produce preferably certain forms (in Obelia 

 3—6 or 9—11 rings). 



We appear to have in regeneration of Obelia at any level a 

 tendency to produce two predominating forms about which the cases 

 group themselves in subtypical "frequency of error" curves. There is 

 a lack of complete blending of one form into the other, similar to that 

 recorded by Bateson *) in the lengths of the forceps of the English 

 earwig and the horns of some beetles. This condition acquires especial 

 meaning in the light of Galton's ideas concerning the significance of 

 organic species as conditions of greater stability. 



1) W. Bateson, On some cases of variation in secondary sexual 

 characters, statistically examined. Proc. Zool. Soc. Lond., 1892, p. 585. 



