256 C. M. CHILD. 



Those mesenteries which extend into the piece undergo re- 

 gressive changes, losing their thickened margins and filaments at 

 the oral end, and become united with the new oesophagus. 



THE APPEARANCE OF THE LABIAL TENTACLES AND THE LATER 

 STAGES OF ORAL REGENERATION. 



The marginal tentacles continue to increase rapidly in length 

 and the oesophagus extends further across the disc from the di- 

 rective side and also becomes deeper. 



Fig. 22 is drawn from a stage three days later than Fig. 

 2O (nine days after the operation). Comparison of this figure 

 with Fig. 20 shows at once the increased diameter of the disc, 

 the greater length of the tentacles, and the marked change in the 

 size and shape of the mouth opening. The tentacles in Fig. 

 22 are still of about equal size and length, except the directive 

 tentacle, which is somewhat thicker and longer than the others. 

 They still retain, to a large extent, the arrangement in a single 

 row, though here and there a few have been forced out of line. 



Upon the disc and forming a circle about the mouth appear 

 the earliest stages of the labial tentacles. They are at this time 

 mere buds, less than one half millimeter in length. All appear 

 nearly simultaneously and develop with equal rapidity. As 

 noted above, they are fewer in number than the marginal ten- 

 tacles, some of the intermesenterial chambers possessing none. 



A view of half the oral end at the stage of Fig. 22 after longi- 

 tudinal section in the directive plane is shown in the schematic 

 Fig. 23. In this case the plane of section passed through one 

 of two small tentacles in the growing region opposite the direc- 

 tive tentacle ; the section of this tentacle (on the right of the 

 figure) is thus considerably smaller than that of the directive 

 tentacle opposite. Comparison of Figs. 21 and 23 shows the 

 changes which have occurred during the three days elapsing be- 

 tween the two stages. The cesophageal invagination is much 

 deeper, the opening to the enteron is larger and the area of 

 growing tissue, including the reduced body-wall, is much greater. 

 From this time on the course of regeneration consists in the 

 gradual increase in size and the pigmentation of the regenerated 

 parts in the manner characteristic of the species. 



