Compensatory Regulation. 



63 



cates, the one of the other, but in others one operculum was 

 considerably larger than the other, though both showed the true 

 "functional" characters. The extremes of the different cases are 

 given in the accompanying figure. (Fig. 22.) 



The resultant opercula usually differed from the normal func- 

 tional one in being shorter and stubbier than the latter. It is to be 

 noted that two fully developed opercula of the kind indicated can 



a a' 



Fig. 22. 

 Hydroides dianthus. Opercula as regenerated at the anterior end of the posterior piece after trans- 

 verse section in the thoracic region (X 17). Left, case with equal opercula. Right, case with unequal 

 opercula. 



be of little value in closing up the opening of the tube as each one 

 stands in the way of the other. The animals in the experiments 

 were, however, not kept in their tubes so that the actions under 

 such circumstances were not observed. It seems that the anterior 

 missing segments were not regenerated in any case. Whether 

 such regeneration would be possible under favorable conditions 

 cannot be said. In my specimens bacteria and infusoria 

 developed on the tender regenerating tissues and the growth 

 was retarded and finally stopped. 



The main point as regards the opercula made out in the group 

 of experiments where the body was cut in two in the thoracic 

 region is this: When the opercular huds have an equal start in 

 development both develop into functional opercula. 



