Vol. 1 1. Mai'di, iqo-f.. No. 



BIOLOGICAL BULLETIN 



NOTES ON REGENERATION. 



T. II. MORGAN. 



During the past summer I made at Woods Holl a number of 

 observations and experiments on the regeneration of several 

 animal forms. The results are here brought together, although 

 they have little more in common than that they all deal with 

 problems of regeneration. 



THE LIMITATION OF THE REGENERATIVE POWER OF 

 DENDROCOZLUM LACTEUM. 



The fresh-water planarians show such remarkable powers of 

 regeneration that it is surprising to find in one of them, Dcndro- 

 cceluni lacteuui, that this power is much reduced. The question 

 at once arises whether we can discover anything peculiar in the 

 relation of this planarian to its surroundings, or in its internal 

 structure that will give a clue to its exceptional behavior. 



There is nothing in its habitat to suggest that it has lost, or 

 has never acquired to the same degree, the power of regeneration 

 possessed by other planarians. In the pond at Falmouth where 

 I collected this species there were also present, sticking to the 

 under surfaces of the same stones, both Planaria maculata and 

 Phagocata gracilis. If Dendroccelumis not as subject to injury 

 as are the other two species, and if, therefore, it does not need 

 the same .regenerative power, it is remarkable that Dendroccelum 

 should be so uncommon in comparison with the other two forms. 

 If it is subject to greater injury, then it has not acquired the 

 power to meet the situation as have the other species. Consider- 

 ations of this kind do not have, I believe, any real bearing on the 

 question of whether an organism has or has not acquired the power 

 to regenerate, although some biologists lay great stress on this 

 sort of speculation. The limitations in the power of regenera- 

 tion of Dendroccelum are peculiar. Lillie found that when only 



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