Compeiisatory Regulation. 6 1 



In Group III, consisting of accurately determined levels, four of 

 the five cases showing valid results developed two functional oper- 

 cula, the fifth one showed a reversal of the opercula. 



In Group IV, also consisting of accurately determined levels, 

 five cases showed a clear result and all of them had a reversal of the 

 opercula. 



The result is a peculiar one in that the most distal and the most 

 proximal groups agree in giving rise to a reversal of the opercula, 

 zuhile the intermediate two groups give rise in a majority of the 

 cases to tivo functional opercula. 



An attempt at an explanation is hazardous and can be little more 

 than a guess. Such a provisional attempt may, however, be made, 

 for by so doing some light may be thrown on the regulation of the 

 "normal" condition in the animal. An examination of the whole 

 number of cases where both opercula are cut ofi^ shows that in all 

 but two the rudimentary operculum after regeneration did not 

 stop at the rudimentary stage but kept on developing until it 

 reached the functional stage. The difference in the resuks is then 

 due to difi^erences in the regeneratory development of the old func- 

 tional operculum. What factor or factors hold it in the rudimen- 

 tary stage in some cases, while in others it is allowed to develop 

 into a full-sized functional organ ? Two factors are to be con- 

 sidered: first, the influence of the position of the cut upon the 

 initial stages of change in the embryonic tissue in the neighbor- 

 hood of the basal suture and, second, the possibility of a retard- 

 ing influence emanating from the new functional operculum 

 which is rapidly developing on the opposite side from the stump 

 of the old rudimentary. 



First Factor. It has been shown above (p. 58), in the series of 

 experiments with an uninjured rudimentary operculum, that 

 injury to the extreme distal portion of the functional operculum 

 does not lead to the dropping off^ of the injured organ or to the 

 development of the opposite rudimentary operculum into a func- 

 tional. Further, from the same series of experiments it is seen 

 that the development of the opposite rudimentary operculum is 

 more easily induced by a terminal injury to the old functional than 

 is the dropping off of the old functional stalk. The latter point is 

 well illustrated by several cases in which the injured stalk remained 

 attached to the animal while the opposite rudimentary had already 

 developed into a full sized new functional. From these data we 



