Regeneration in Hydromcdusae 25 



perisarc. The proximal tentacles develop first, the development 

 beginning at the distal end. 



6. In Tuhularia tenella the first part of the regeneration is 

 similar to that in T, crocea. The hydranth body is separated 

 from the stem by a constriction before the tentacles begin to 

 develop. Tentacles appear as rather short buds, the final form 

 and size being assumed by new growth after the hydranth 

 emerges from the perisarc. 



7. In Tnhnlaria larnyx there is a tendency for hydranths to 

 regenerate at both ends of the stem, and there is no difference 

 in the time of their development. The first stage of regeneration 

 is the emergence of the coenosarc from the old perisarc, and 

 the secretion of a new perisarc around the protruding part. A 

 few annulations are always present close to the old perisarc. 

 Circulation of fluid and deposition of pigment are similar to 

 that in T. crocea. Tentacle anlagen are much longer than in T. 

 crocea, and often twined spirally around the coenosarc. Ten- 

 tacles assume their final form and size while still within the 

 perisarc. Gonads may begin to form before the hydranth 

 emerges from the perisarc. 



8. Eudcndrinni rauiosiini, E. disbar, Pcnnaria fiarclla. and 

 Tnhnlaria crocea were successfully grafted, union taking place 

 equally well, whether the distal ends or the proximal ends were 

 joined, or whether distal end was grafted to the proximal end. 

 No union of Endendrimn raniosnni and E. dispar was secured, 

 nor of Eudcndrinni and Pennaria. 



g. In Tnhnlaria crocea the distal tentacles form by the sepa- 

 ration from the entoderm layer of a rod or column of entoderm 

 cells which are surrounded by the ectoderm to form the tentacle. 

 Proximal tentacles form by a complex folding, involving both 

 ectoderm and entoderm, the ectoderm gradually surrounding the 

 entodermal fold and separating the tentacle from the hydranth 

 body. 



10. Distal tentacles of Tnhnlaria tenella form as in T. aocea. 

 Proximal tentacles develop partly by evagination of the ento- 

 derm and later by a new growth after the hydranth emerges from 

 the perisarc. 



299 



