260 C. M. CHILD. 



4. The regenerating marginal tentacles appear at first in a 

 single circle and all usually regenerate with nearly equal rapidity, 

 except in some cases the youngest pair in the growing region. 

 The directive tentacle is usually slightly thicker than the others 

 since the directive mesenteries are somewhat farther apart than 

 the other mesenteries. Rapid increase in length occurs in the 

 marginal tentacles, and the arrangement in about three circles or 

 rows is gradually attained in consequence of the fact that there 

 is not sufficient space on the margin of the disc for all of the ten- 

 tacles in a single row ; some are forced peripherally by the mu- 

 tual pressure exerted. 



5. As the tentacles grow the disc expands and the distinction 

 between the thin membrane of new tissue which first closed the 

 end and the old body-wall with which it was connected disap- 

 pears completely in consequence of the complete disappearance 

 of the muscular layer, the reduction in thickness, and the loss of 

 pigment in the body-wall of the oral end. 



6. The mouth appears after the marginal tentacles are well 

 established near the base of the directive, tentacle, gradually 

 extending along the directive plane across the center of the disc 

 until it is symmetrical. The part of the mouth first regenerated 

 is the region of the siphon oglyph. 



7. The labial tentacles do not appear until the marginal ten- 

 tacles have attained a length of several millimeters. Each ten- 

 tacle appears as a distinct bud over an intermesenterial chamber, 

 but some intermesenterial chambers are without labial tentacles. 



8. After the aboral end is closed by the new tissue this slowly 

 acquires a conical form, protruding from within the wrinkled 

 margin of the old body-wall. The wrinkles on the latter gradu- 

 ally disappear and the pigmentation slowly fades out for a short 

 distance oral to the cut end, this change being connected with re- 

 duction and disappearance of the muscular layer as this region of 

 the body-wall becomes involved in processes of growth and redif- 

 ferentiation in the same manner as the oral end. The aboral end 

 grows out into an elongated conical form at the end of which 

 the aboral pore appears. As the new muscles differentiate in 

 this region pigment stripes begin to appear. 



HULL ZOOLOGICAL LABORATOR-*, UNIVERSITY OF CHICAGO, 

 July, 1903. 



