266 C. M. CHILD. 



According to this view these cases are merely special cases of 

 more or less complete local closure of the enteron by inrolling. 

 Various experiments of similar kind have already been described 

 (Child, '04^). The only difference between those and these is that 

 here the inrolling is transverse across the oral end and conse- 

 quently permits the appearance of tentacles upon the whole in- 

 rolled portion. Fig. 2 shows the condition of the end after the 

 regeneration of tentacles has begun. By this time the mesen- 

 teries in the region of the inrolled margin have acquired new 

 relations to the body-wall such that the margin is held in position. 

 The reduction in thickness of the wall in the upper portion of the 

 inrolled region icpresents the beginning of tentacle formation. 

 In every case of this kind which I have observed conditions have 

 been similar. The only conclusion possible is that Loeb's state- 

 ment that the tentacles arise from the cut surface is incorrect and 

 that in the pieces shown in his Figs. 46 the tentacles arose in 

 the manner which I have described. 



If my explanation is correct, then the results obtained from 

 these open pieces do not contradict the conclusions of my previous 

 papers, viz., that internal water-pressure constitutes a factor in 

 tentacle-regeneration. As regards local pressure due to circu- 

 latory currents and its possible effects the statements made in 

 previous papers (Child, '04^, '04^, '04^) will apply here. 



In all pieces of this kind the appearance of the tentacles is 

 much delayed and their regeneration is very slow. In no case 

 observed do they ever attain more than a small fraction of the 

 normal length. They are, moreover, always more or less blunt 

 and frequently very irregular, i. e. t of different lengths. Similar 

 characteristics were described and discussed for certain cases in 

 C. solitaries in a previous paper (Child, 04*:). Thus in C. i/ian- 

 branaceus as in C. solitaries the facts indicate that internal pres- 

 sure plays an important role in tentacle-regeneration. 



THE REDUCTION OF NORMAL TENTACLES. 



Not only was it possible to retard or inhibit the regeneration 



of tentacles by reduction of the internal water-pressure, but it 



was found that fully developed tentacles could be reduced in 



length by reducing the internal pressure. This process of re- 



