THE DYNAMIC FACTOR IN REGENERATION. 



T. H. MORGAN. 



With the publication of the data here presented the series of 

 experiments that I have carried out on Tubularia for several 

 years may be considered as temporarily brought to a close. I 

 take this opportunity therefore to sum up the evidence bearing 

 on the problem of the formative factors of regeneration, as ex- 

 hibited by this hydroid. In the course of my experiments ten- 

 tative hypotheses have been proposed here and there that have 

 at least served to suggest further experiments. The conflicting 

 evidence sometimes inclined me towards one point of view, some- 

 times towards another ; yet, all in all, the same general line of 

 thought, if sometimes vague, can be traced through the attempts 

 to analyze the results. It will be my endeavor here to bring 

 more into the foreground those theoretical deductions that seem 

 to me at present to be best in harmony with the experimental 

 evidence. 



That the dynamic factor in regeneration is not primarily the 

 outcome of physiological movements of the animal, or of its 

 parts, is made probable not only by many facts familiar to every 

 student of regeneration, facts that show that the new part often 

 develops under conditions where movement or function in this 

 sense is absent, but also by the important experiments of Zeleny 

 and of Stockard with the jelly-fish Cassiope. They have shown 

 that when one half of the disc is brought to rest by removing 

 the sense organs (and scratching a barrier zone across the con- 

 necting ectoderm) the quiescent half regenerates as well and as 

 rapidly as the half left pulsating during the period of regeneration. 



Since every part of the stem of Tubnlaiia is capable of pro- 

 ducing a hydranth the inhibition of basal development is obviously 

 due to the presence of a hydranth or of a developing hydranth 

 at the oral end. Two alternative chemico-materialistic explana- 

 tions have been suggested for cases like this. (A) The oral 

 hydranth may use up some materials necessary for the formation 



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