252 C. M. CHILD. 



mesenteries beneath advances. In Fig. I 5 the ridge is shown as 

 slightly lighter in color than the rest of the body. The pigmen- 

 tation is beginning to disappear. Most of the stripes can still be 

 followed over the ridge to the margin of the old tissue, but upon 

 the ridge they are fainter than before. Fig. 16 shows a portion 

 of the end at a slightly later stage, more highly magnified. Here 

 the lighter color of the ridge is more distinct. While the body 

 in general retains its brown color the ridge becomes light yel- 

 lowish and its pigment disappears completely in the course of a 

 day or two. 



This change in pigmentation indicates that some alteration in 

 the tissues is occurring, and the nature of the alteration becomes 

 evident when a longitudinal section through the end (Fig. 17) is 

 examined. This figure shows that the thickness of the body- 

 wall and especially of the muscular layer is decreasing consider- 

 ably in the region corresponding to the ridge. This decrease is 

 shared to a certain extent by the ectoderm and entoderm as the 

 figure indicates. The new regenerating mesenteries are minute 

 folds in the infolded region, ending free aborally (;;/, Fig. 17). 



This ridge in which loss of pigmentation and reduction in thick- 

 ness of the body-wall are taking place may be designated as the 

 marginal tentacular ridge, since it is from this that the marginal 

 tentacles arise ; indeed the reduction in thickness of the body- 

 wall and the division of the ridge into areas corresponding to 

 the intermesenterial chambers are the preliminaries of tentacle 

 formation. 



The marginal tentacles do not arise from the cut edge of the 

 body-wall itself but a short distance away from it, viz., at the 

 highest point of the ridge (/, Fig. 16), /. e., entirely within that 

 portion which was originally part of the body-wall and not in 

 the new tissue which closes the end. 



Fig. 1 8 shows the oral end of a piece about a day later than 

 the stage shown in Figs. 15 and 16. Here the new marginal 

 tentacles are distinct and are evidently increasing in length. The 

 pigment has disappeared completely from the tentacular ridge 

 which is now whitish in color and distinctly translucent. Some 

 of the tentacle buds are slightly broader than others owing to 

 the fact that in the infolded condition of the margin some inter- 



