58 Charles Zeleny. 



The changes taking place on the other side of the body are v-ery 

 evident 3 or 4 days after the operation, often before the rema- 

 nent of the functional stalk has dropped off. This fact that the 

 rudimentary operculum begins to develop even before the func- 

 tional has dropped off seems to argue against the mere retarding 

 influence of the organ as a mechanical v^^eight, though of course 

 the weight is considerably diminished by the removal of the part 

 of the operculum distal to the cut. The stages through which the 

 rudimentary operculum passes in changing into a functional one 

 are given in the accompanying figures. (Fig. 19c, a-d.) The 

 essential points to be emphasized in this development are: first, the 

 fact that throughout there is no sign of the appearance of special bran- 

 chial characters, and, second, that the secondary processes of the 

 operculum appear before the primary ones. The regeneratory 

 development, therefore, differs widely from the ontogenetic or 

 probable phylogenetic one as regards these points. 



A series of operations was performed on the functional opercu- 

 lum to determine the amount of injury necessary to bring about 

 reversal. The cases overlap slightly but it is found that in general 

 the cutting off of the distal circlet of processes does not induce 

 reversal while cuts through the main enlarged portion of the oper- 

 culum bring about a reversal of the opercula. In one case the 

 stalk of the injured operculum remained attached though the rudi- 

 mentary operculum in the meantime had reached a stage equal to 

 three-fourths of the normal functional development. It may be 

 concluded that a removal of the secondary circlet of processes of the 

 functional operculum does not as a rule cause reversal, while a 

 similar injury below this point to the main portion of the cup or to 

 the stalk of the operculum always brings about such a result. 



d. Operations on Rudimentary Operculum. When the rudi- 

 mentary operculum alone is removed there is no effect upon the 

 functional operculum and a new rudimentary develops in place of 

 the old one which had been cut off. The cut end rounds off, a 

 bud-like mass of new tissue appears there, and the whole, both 

 old and new tissue together, gradually assumes the shape of 

 the old rudimentary operculum. The greater part of the change 

 from the beginning is, however, accomplished by the growth of 

 new tissue and only very little by the change in form of the old. 

 No further development takes place. The result is the same no 

 matter what the level of the cut may be. One of the levels at 



