RE GEN ERA TION 



r\ 



turn 



FIG. 25. Piece of stem of Tubular ia mesembry- 

 anthemum split in two lengthwise. Forma- 

 tion of whole hydranth that turned away 

 from contact with old perisarc. 



the piece, we can account for the 

 results. On this hypothesis the 

 action of the water on the free 

 end need not be a factor in the 

 result, but the oblique end is itself 

 sufficient to determine the series 

 of regulations, or mass-relations, 

 that lead to the laying down of 

 an oblique hydranth. 



When the hydranth protrudes 

 from the stem it assumes an 

 oblique position, as shown in Fig. 

 20, A 1 . Driesch supposed the 

 oblique position of the hydranth 

 to be due to an oblique zone that 

 develops behind the hydranth, but 

 the result can best be explained, 

 as certain other experiments that 

 I have made seem to show, as 

 due to the negative thigmotropism 

 of the hydranth at the time it pro- 

 trudes from the old perisarc. It 

 turns away from the projecting 

 side of the oblique end of the 

 perisarc, as it does from any solid 

 body with which it comes in con- 

 tact. That this is the case is best 

 shown by splitting the stem length- 

 wise into halves. In this case, 

 although the two circles of ten- 

 tacles may be laid down squarely 

 (Fig. 25, A), the new hydranth 

 protrudes at right angles to the 

 old perisarc, as shown in Fig. 

 25, B. 



THE INFLUENCE OF INTERNAL ORGANS AT THE CUT-SURFACE 

 ON THE NEW STRUCTURE 



In a few cases it has been discovered that the presence of certain 

 organs at the exposed surface is necessary in order that regenera- 

 tion may take place. The following experiment that I have recently 

 carried out shows, for instance, the influence of the nerve-cord on 

 the regenerating part. A fev/ of the anterior segments of the earth- 



