142 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vol. 45 



where, that the position of regenerating tentacles is determined in 

 this manner. 



It is possible also to reduce the fully grown tentacles of normal 

 animals to mere stumps by keeping the aboral end of the body con- 

 tinuously open. After the tentacles have remained collapsed for a 

 time, the tips begin to shrivel and are gradually absorbed until only 

 stumps remain. If, now, the aboral end of the body be allowed to 

 close, the enteron once more becomes distended with water, and the 

 tentacles, being again distended, gradually grow out again. Many 

 other instances of the close relation between growth and the pres- 

 sure of the water in the enteron were observed, but their description 

 must be deferred. 



The chief results of my work on Cerianthus may be summed up 

 in the statement that regeneration in Cerianthus is influenced in large 

 measure by simple mechanical conditions of pressure and tension, 

 and that in the absence of these conditions in typical amount and 

 localization, typical regeneration is impossible. 



IV. TUBULARIA 



A part of the work on Tubular ia consisted of the reexamination 

 of certain regulative phenomena described by other investigators. 

 My conclusions differ from theirs in various points, but a critical dis- 

 cussion may be omitted here. 



A few points of interest which are either new in themselves or 

 afford new interpretations of known facts may be mentioned briefly. 

 It was found that in many instances the pieces cut from the stems 

 of Tubularia would produce a stolon at the aboral end, and if they 

 were in contact with a solid body would become attached in a few 

 days. In many cases these stolons attained a length of fifteen milli- 

 meters or more and frequently became branched. In the course of 

 time most of the branches of the stolon, and often even the tip of the 

 main stolon, turned upward away from the substratum and developed 

 new hydranths in the usual manner. If the stolon did not come 

 into contact with a solid surface within a day or two after its forma- 

 tion, the end usually produced a new hydranth in a much shorter 

 time than when it succeeded in attaching itself to a surface. This 

 power to produce stolons is found only in the more vigorous stems, 

 and long pieces are more likely to produce stolons than short pieces. 



The formation of a hydranth at both oral and aboral ends of pieces 

 from the stem of Tubularia, or the formation of a hydranth at the 

 oral end and nothing at the aboral end, have been described by a 



