FORM-REGULATION IN CERIANTHUS. 1 09 



ever, that the production of these supplementary discs and ten- 

 tacles at any level of the body capable of growth is possible 

 without the presence of a cut surface, and I predict that as soon 

 as a method is devised for retaining a sufficient local constriction 

 at the same level for a -few days without causing injury to the 

 body-wall, the production of tentacles without relation to cut sur- 

 faces will be possible in Ccrianthus. 



Like the tentacles on the lower margin of an oblique piece 

 (Child, '04^), the tentacles below a lateral cut when once growth 

 has begun, continue to grow even though the animal is removed 

 from the netting. By this time union of body-wall and mesen- 

 teries in the new relations is sufficiently advanced to cause the 

 persistence for a time of the fold formed by the netting. In most 

 cases, however, the fold is gradually obliterated by the internal 

 pressure and the supplementary disc protrudes from the side of 

 the body (Fig. I 5). 



Loeb called attention to the fact that only those supplementary 

 discs which are situated near the oral end ol the body possess 

 mouths, the others consisting merely of a partial ring of tentacles 

 arising from a small surface resembling part of a disc but com- 

 pletely closed. Comparison of Figs. 2, 3, 4, 6, 7, 8 with Fig; 

 i 5 will show the difference in character of the supplementary 

 structures at different levels. It is evident at once that the 

 presence of the oesophagus is responsible for the formation of the 

 new mouth in supplementary discs near the oral end. Aboral to 

 the oesophagus there is nothing with which the cut edges of the 

 body-w r all can unite to give rise to a new mouth. If a cut passing 

 nearly through the body is made aboral to the oesophagus then the 

 in rolled cut margins aboral to the cut unite with the cut ends of 

 mesenteries over a large part of the circumference and are held in 

 the inrolled position long enough for the formation of a new 

 mouth. As a matter of fact, however, in such cases the part of 

 the body oral to the cut, being united with the aboral portion 

 only by a slender strip of the body-wall; separates after a few days 

 and the regenerating disc is no longer supplementary but terminal 

 on the aboral piece and regenerates in the typical manner. Owing 

 to this separation I have not yet succeeded in bringing about the 

 production of supplementary discs with mouths in the region 

 aboral to the cesophageal region. 



