IOS C. M. CHILD. 



after closure the diameter of the body increases, but the wires of 

 the netting prevent increase in diameter in the region of the cut. 

 The result is indicated by Fig. 13. The thin, delicate new tissue 

 is chiefly affected, being stretched in the direction of the tension, 

 or more probably undergoing rapid growth in response to it. 

 Thus a deep groove is formed on one side of the body and on 

 the aboral side of this groove the new tentacles of the supple- 

 mentary disc appear (Fig. 14). 



Apparently the netting has merely prevented the body-wall 

 from assuming the form shown in Fig. 11, or, in other words, it 

 has prevented the obliteration of the angle in the body-wall due 

 to inrolling, and has in fact made this angle less obtuse (cf. Figs. 

 12 and 13). If this conclusion be correct, and there is little 

 room for doubt, it follows that the appearance of the supple- 

 mentary disc is due, not to the presence of the cut, but to the 

 bending inward of the body-wall in such a manner as to form in 

 longitudinal section an angle opening aborally. But how can the 

 formation of this angle determine this region for the formation of 

 tentacles ? The only answer to this question which seems to me 

 at all satisfactory is the suggestion already made (Child, '04^, 

 'O4<r, '04^) that the circulatory currents passing orally along the 

 body-wall in each intermesenterial chamber strike against the in- 

 rolled body-wall and so produce areas of increased pressure to 

 which the tissues react by growth and tentacles appear. The 

 arrows in Figs. 11 14 indicate these currents. In no case within 

 my experience have tentacles been seen to arise otherwise than 

 on an inrolled portion of the body-wall. Ordinarily of course the 

 inrolled region is a cut edge, but here the cut closed before the 

 inrolling was brought about to any great extent. 



If the formation of the angle in the body-wall instead of the 

 presence of a cut surface is the essential condition for tentacle for- 

 mation, it should be possible to bring about tentacle formation at 

 any level capable of growth by constricting the body just oral to 

 this level. I have attempted many times to carry out experi- 

 ments of this kind by ligaturing the body at some level. All of 

 these attempts have failed because the specimens parted in the 

 plane of the ligature after a few hours if this was tied tightly, or 

 crept out of it if it was at all loose. I am firmly convinced, how- 



