394 



the coenosarc. In my complète paper tlie histology of the proceas 

 will be treated more fully. It is not very différent from the pro- 

 cess of hydranth formation described bv Stevens (01). I should 

 State, bowever, that the first tentacle „Anlagen" appear hère first on 

 the old wall of the stem and afterwards on the closing memljrane. 

 After the formation of the tentacles the hydranth émerges from 

 the perisarc by breaking tbi'ough it. The hydranth with a small 

 pièce of the stem projects at right angle from the perisarc. The 

 interprétation of this position is given by Morgan (01) who con- 

 siders it as „the rcsult of negative stereotropism". 



D ries eh') (00) bas shown that pièces from the oral end 

 of the stem produce hydranths in a shorter time than pièces from 

 the more aboral parts. This fact which I could often observe for 

 the cross -eut pièces cannot be extended to those split lengthwise. 



It is known that the hydranth in pièces eut crosswise deve- 

 lops at first at the anterior end and afterwards a hydranth deve- 

 lops also at the posterior end. The process of the development uf 

 the hydranth at the a))()ral end was discovered bj' Loeb^! who 

 gave the name h e t e r (j m o r p h o s i s to this phenomenon. But we 

 see in the longitudinally split pièces that the hydranth can develop 

 often at first at the aboral end (heteroraorphosis: Loeb, Morgan) 

 or in several cases, as I will describe later, in the middle of the 

 stem. Only when a very small part bas been removed lengthwise 

 fi'om the stem, does the lutter produce the hydranth, first at the 

 oral (anterior) end. In other cases the development of the hydranths 

 at the anterior and posterior end is going on almost simultaneously 

 or at very short intervais from each other. In many cases the 

 hydranth is formed only at one end. 



In those cases in which the stem is split lengthwise the 

 opération brings about, I think, somewhat diflerent internai con- 

 ditions in the living organism. This change carries with it. 

 I think, a change of the factors that hâve a determining influence 

 upon the process of régénération. Therefore the course of l'egene- 

 ration is hère somewhat différent from the process in pièces eut 

 across. 



') Driesch H. Studien über das Regulationsvermiigen der Organismen, 

 Archiv für Entwickelungsmechanik. Bd. IX. 1900. 



') Loeb J. Untersuchungen zur physiologisch&n Morphologie. Würzbnrg, 

 1890. 



