6o 



Charles Zeleny. 



four groups we get a very interesting correlation between the 

 regions and the corresponding results of the operation. In this 

 way we get four fairly well marked groups. Group I consists of 

 accurately located cases near the distal end of the stalk where it 

 expands into the cup. Group II has the earlier cases located from 

 description alone, in most cases stating that the "functional stalk 

 was cut near its middle." Group III has accurately determined 

 cases located about one-fifth of the length of the opercular stalk 

 from the basal suture. Finally, Group IV contains the cuts 

 made just distal to the basal suture. (Fig. 21.) 



Table VIII. Hydroides dianthus. Both Opercula Removed. 



Fx = F2 

 Ri = R2 



F: = R2 



Ri = F2 



F, = ¥2 

 Ri =- F2 



F> = S 

 Ri = F2 



F, = x' 

 Ri = x" 



Group I. 

 Group II. 

 Group III. 

 Group IV. 



Fi^ Original functional operculum. 

 Ri= Original rudimentary operculum. 

 F2= Resultant functional operculum. 



R2= Resultant rudimentary operculum. 

 S = Functional stalk remains attached, 

 r', r"= Small undifferentiated buds of new tissue. 



In Group I the three valid cases (see Table VIII) all showed a 

 reversal of the opercula, the old functional becoming the new rudi- 

 mentary and the old rudimentary becoming the new functional. 



In Group II where the region of the cut was not so accurately 

 located the results are scattering. Seven of the cases give results 

 valid for our purpose. Of these three developed two functional 

 opercula, one showed a reversal similar to that of Group I, one 

 showed the development of a new functional in place of the old 

 and a new rudimentary in place of the old rudimentary, in one the 

 functional stalk did not become detached and the old rudimentary 

 developed into a functional, and in still another case there were 

 rudimentary buds on both sides, neither of which reached a stage 

 beyond a rounded knob and were, therefore, not developed even up 

 to the rudimentary stage proper. 



