THE DYNAMIC FACTOR IN REGENERATION. 267 



of the buds basal to the middle region develop. The presence 

 of growing shoots in the middle of the piece does not inhibit the 

 apical buds from developing, if external conditions are supplied 

 favorable to their growth, but the basal buds are inhibited by the 

 presence of shoots on the more distal parts. These facts are incom- 

 patible with the assumption that the results are due to the pres- 

 ence of materials used up by those parts that develop first to the 

 exclusion of other parts. They also show that the alternative 

 view is untenable, for, the presence of growing shoots in the middle 

 of the piece is not antagonistic to the development of shoots in 

 other regions provided those regions are situated more distally. 



In the case of Tubularia, it is more difficult to present con- 

 vincing evidence that distal hydranths do not produce ma- 

 terials inhibiting the development of basal hydranths, improbable 

 as such an interpretation may now seem. But the fact that basal 

 hydranths do develop after the oral hydranths have formed may 

 seem to discredit this view. Here, however, an apparent para- 

 dox is found. The experiments seem to show that when the 

 oral hydranths develop, the basal hydranths are retarded in de- 

 velopment, but they do develop later, and the results also show 

 that if both start simultaneously both develop at the normal rate. 

 The paradox is due, I think, to two antagonistic factors at work 

 at the same time. Admitting that the oral development tends to 

 inhibit the beginning of basal development, we also find that if 

 other influences suffice to start both simultaneously, the on-rush, 

 so to speak, of the process once begun changes the conditions 

 that tended to prevent the starting. Strange as this seems it is 

 little more than a statement of the facts. The same results may 

 be put in a somewhat different way. A cut end being present, 

 whether oral or basal the conditions that call forth hydranth 

 formation are given. Experiments show that the oral end 

 tends to develop first, its development acts as a partial inhibition 

 of the basal hydranth-formation. If this influence is strong 

 enough the basal development is temporarily held in abeyance, 

 but if not the inhibition is overcome. Once overcome, the for- 

 mative influences do not check the further action of the basal 

 end. In this connection it is curious to note that small oral 

 pieces produce simultaneous hydranths more often than larger 



