38 



Charles Zeleny. 



functional operculum, but in addition to it there is an added rudi- 

 mentary operculum with its point of attachment posterior to that 

 of the functional. This added rudimentary operculum agrees in 

 all respects with the one on the opposite side, so that we have two 

 rudimentary opercula and one functional one. The specimen 

 indicates that the influence which determines the development of 

 a functional or a rudimentary operculum is not always a bilater- 

 ally diff'erentiated one. A more complete discussion must be 

 reserved until the experimental data have been given. 



2. Developjnent of Opercula. 



I. Ontogenetic Development. 



a. Introduction. In a paper, entitled "A Case of Compensa- 

 tory Regulation in the Regeneration of Hydroides Dianthus," I 



described some experiments 

 showing that when the func- 

 tional operculum of this 

 Serpulid is removed the 

 rudimentary operculum on 

 the opposite side develops 

 into a new functional oper- 

 culum similar to the old one 

 while in place of the old 

 functional stalk a new rudi- 

 mentary bud develops. In 

 the discussion of this and 

 similar experiments it was 

 stated that a knowledge of 

 the ontogenetic development 

 of the organ is highly desir- 

 able before we can be in a 

 position to discuss the data 

 in their full relations. With 

 this object in view the writer 

 undertook to raise the larva up to the stage where both opercula 

 have attained their normal adult development. 



In attempting a provisional explanation of the compensatory 

 regulation of the opercula it was stated in the above paper that 

 there may be a restraining influence exerted by the fully developed 



Fig. 9. 

 Hydroides dianthus with three opercula, two rudi- 

 mentary and one functional. Note that one of the 

 rudimentary opercula is attached near the base of the 

 functional one ( X 15). 



