54 Charles Zeleny. 



kept in dishes in the laboratory exhibited physiological reversal 

 were negative, although the time was in all cases too short to 

 constitute a good test. There was no change in any case unless 

 the functional operculum was injured. However, the very near 

 equality between right and left-handed individuals seems to pre- 

 clude the possibility of all reversal being due to injury of the func- 

 tional operculum. And we have beside the analogous case of 

 physiological reversal in the young animals as has been empha- 

 sized before. 



2. Regeneratory Development. 



a. Introduction. The nature of the opercular modifications 

 among the Serpulids has now been outlined in the discussion of the 

 comparative anatomy and their origin within the individual life 

 history has been traced in the genus Hydroides. There now 

 remains an attempt at an experimental analysis of the factors 

 involved in the development and maintenance of the adult charac- 

 ters. Partly because of the imperfection of the method and 

 partly because it is not desirable to dissect the data too minutely 

 while presenting them, the latter will be given in the descriptive 

 portion of this section as parts of individual experiments without 

 perfect regard to logical development of the analysis of the factors 

 involved. The latter will be attempted more fully in the general 

 discussions to follow the descriptive portions. 



In a former paper a preliminary report of some of my experi- 

 mental results on compensatory regulation in the regeneration of 

 Hydroides dianthus was given. Since that time a more detailed 

 series of experiments has been undertaken along the same lines 

 and the work has been extended to other species of the family. 

 Two distinct problems have come up. In the first place is the 

 study of the factors involved in the compensatory regulation of 

 the opercula which, as stated above, is the main object of the 

 present paper. In the second place a comparison of the regen- 

 eratory development of the opercula with the ontogenetic and 

 with the probable phylogenetic development brings up an ex- 

 tremely interesting discussion with important bearings on the 

 recapitulation theory. 



The great majority of the experiments were performed on 

 H. dianthus and this form will be discussed first. Then will 

 follow the other members of Group V, namely, H. uncinata. 



