1 8 Charles Zehnw 



III. THE OPERCULA OF 5ERPULIDS. 



We have now considered a case (section one) in which there is a 

 readjustment in the uniniured portions of a svstem as a tesult 

 of their mutual interaction. This interaction is not compHcated 

 bv the addition of a regenerating organ. The result is a new 

 svstem in equilibrium, based on the resultant of the interactions 

 of the uninjured parts. 



In a second section (section two) a case was considered in which 

 it was possible to studv the effect of the presence or absence of 

 uniniured portions of the animal upon the rate of regeneration of 

 the removed ones. The reaction is here more complicated than 

 in the tirst case, because there mav be here an action of other 

 regenerating surfaces upon anv particular wounded surface as 

 well as the action of the uninjured organs themselves. 



In the present section (section three) a case wiU be considered 

 in which there are two organs, dissimilar in size, situated on mor- 

 phologicallv similar opposite sides of the median line. An 

 extremelv close interaction is found to exist between these two 

 organs so that anv disturbance in one is reflected in changes in 

 the other. This close interrelation between the opercula of the 

 Serpulids. the organs in question, gives a good basis for the studv 

 of such interactions as were outlined in the general introduction. 

 The opercula of the Serpuhds furthermore furnish exceptionallv 

 good material for this studv of compensators* regulauon because 

 of the various decrees of asvmmetrv present in the different 

 species. 



In the following account it will be necessan" to go into paths 

 not in the line of the main discussion, but such a course cannot be 

 avoided in a studv of the factors controlling the regulation of the 

 opercula. 



In the adiik Serpulids of the genus Hvdroides we have an 

 asvmmetrical stable svstem with the funcrional operculum on the 

 right side and the nidimentan' operculum on the left or vice versa. 

 The nature of this case will first be taken up. Then the opercula 

 of other members of the familv will be described. This will be 

 followed in turn bv a description ot the ontogenetic development, 

 the regeneratorv development, some speculations as to the prob- 

 able phvlogenetic development, a discussion on the comparison 

 of regeneratorv, ontogenetic and probable phvlogenetic develop- 



