Compensatory Regulation. 71 



The interesting general point is that regeneration takes place from 

 the cut surface without a breaking off at the basal suture. 



When the operculum was pulled off at the time of removal of the 

 animal from its tube the break always took place at the A-shaped 

 suture and the regeneration then naturally followed from this 

 level. 



In a third set of experiments the animal was cut in two in the 

 thoracic region. All such specimens, however, died before the 

 appearance of regeneratory changes. 



The operculum was removed in five specimens of Ver- 

 milia multivaricosa. In no case was there any regeneration of the 

 organ. In one individual the cut was made through the narrow 

 portion of the stalk just below the terminal cup. In this case 

 (Fig. 24F), two days after the operation, there was a protruding 

 knob on the median side of the stalk which may represent the 

 beginning of an opercular regeneration, such as that shown in the 

 case of Ditrupa. (Fig. 24.) In the other four specimens the cut 

 was through the cup portion of the operculum. In all of these 

 there was no regeneration, though three of them lived more than 

 eleven days after the operation. 



k. Discussion of the Data. It has been seen that the char- 

 acter of the regeneratory process varies according to the loca- 

 tion of the cut. When the regeneration takes place from the 

 breaking joint of the operculum (Hydroides, etc.) or of the 

 branchial circlet (Apomatus) the regeneration is highly special- 

 ized and the stages do not follow the ontogenetic ones very 

 closely. When, however, the regeneration is from a thoracic cut, 

 where the branchial and opercular tissues are not as highly special- 

 ized with respect to the mechanism of regeneration, the organs pass 

 through a stage which may very well be compared with a corre- 

 sponding stage in the ontogeny of Hydroides. However, even 

 here the regeneratory development does not follow the other 

 closely because the operculum is very evidently differentiated as 

 such from the start in regeneration though not in ontogeny. 



Our general conclusion may, therefore, be that when there is no 

 definite mechanism for the autotomy of a region of the body the 

 regenerating tissue may in its various stages resemble ontogenetic 

 stages quite closely, but where a definite mechanism is present the 

 resemblances are much less close, the development being hastened 

 in the latter as compared with the former and both being hastened, 



