AUTOTOMY OF HYDRANTH OF TUBULARIA. 173 



Cerfontaine 1 and by Cast and Godlewski. 2 Cerfontaine believed 

 that the cause of the absorption lay in the difficulty with which 

 the fully formed hydranth responded to sudden changes in its 

 environment, whereas the regenerated ones are better adapted 

 by " une acclimation rapide." 



Cast and Godlewski (/. c.) have examined the case more 

 critically. They show that, at the beginning of the process, the 

 tentacles are withdrawn until nothing is left externally to show 

 where they once existed. The peristome likewise disappears and 

 the mouth closes. Ultimately, all that is left of the hydranth 

 is a small smooth knob. This, too, becomes absorbed into the 

 stem and a cicatrix alone remains. Then regeneration may 

 begin. Concomitant with these external changes, the cells of 

 the endoderm begin to dissociate and disintegrate and come to lie 

 as detritus in the lumen of the hydranth. The current flows 

 down into the stem and carries the debris and this continues until 

 the whole of the hydranth has been absorbed. The changes in 

 the cells are not restricted to the endoderm cells for those of the 

 ectoderm lose their vacuoles and become greatly reduced in size. 

 They remain, however, much longer in situ than the cells of the 

 endoderm. The changes seem to affect, from the first, all of 

 the cells of the hydranth and the process is only in this sense a 

 local one. Moreover, inasmuch as open communication between 

 the hydranth and the rest of the stem is maintained, it cannot be 

 urged that the process is a passive one, due simply to the death 

 of the cells of the hydranth. In this respect, the description of 

 Cast and Godlewski is similar to that to be given for Tnbnlaria. 



The first evidence of autotomy in Tubularia is the sinking of 

 the hydranth upon the stem. This pendent position results from 

 a constriction of the coenosarc at the base of the hydranth, w r here 

 it joins the stem. For a time the hydranth hangs suspended by 

 the perisarc, but soon this breaks and the hydranth falls. During 

 the whole of this process, including, generally, the first half hour 



1 Cerfontaine, P., " Recherches experimentale sur la regeneration et 1'hetero- 

 morphose chez astroides calycularis et Pennaria carolinii," Arch, de Biol., t. 

 19, 1902. 



2 Cast, R., und Godlewski, E., Jr., " Uber den Regulationserscheinungen hei 

 Pennaria carolinii," Arch, fiir Entwickelungsmec., Bd. 16, 1903. 



