393 



ectoderm begins to overgrow the endodermal cells which are ai- 

 ranged in several layers; soon altei-wards this endodermal tissue 

 becomes surronnded by the ectodermal layer. The process of the 

 disintegration and the production of the globules begins at several 

 places in the endodermal layer (fig. 8), while the overgrowth is 

 taking place. Later a circulation of the globules appears, and the 

 cavity arising from degeneration of several cells becomes vvider 

 At last only two layers bounding the 

 cavity reiiiain: the endodermal cells 

 forming the inner and ectodermal the 

 ou ter layer. 



Whence arises this considérable, 

 number of endodermal cells in the early 

 stages of formation? An examination Fig. 8. 



of thèse pièces of the stem after the 



formation of the new cavity gives évidence in favour of the view 

 that the arrangement in several layers of the endoderm is the resnlt 

 of the migration of the cells from oral and aboral end to the middle 

 part of the pièce; we tind at both ends only the perisarc while the 

 coenosarc was accumulated in tbe more central part of the half- 

 cylinder (comp. Morgan') (01) fig. 25. p. Ô2). The new cavity 

 which is formed in thèse cases is not the old cavity closed by the 

 regenerative process. but an entirely new canal which is formed 

 from the tubularian stem. 



If the stem of tubularia is split lengthwise into unsymmetri- 

 cal fjieces whicli bave in one place narrower, in annther place broader 

 walls, the manner of the formation of the cavity is dépendent on 

 the relative thickness of the diô'erent régions. The closing in the 

 différent régions follows one or the other of the précèdent methods 

 of closiire according to the breadth of the région. 



The first Anlage of the hydranth appears 2 to 4 days after 

 the opération. Within thèse limits the time is variable and is al- 

 ways longer than in pièces split crosswise. 



The part where the hydranth develops thickens and soon 

 afterwards the tentacle „Anlagen" appear as longitudinal folds of 



') Morgan H. T. Kegeneration. New-Vork. The Macmillan Company. 1901. 



