1 6 C. V. MORRILL, JR. 



From the foregoing facts, the lack of regeneration of the 

 paired fins in so many cases is seen to be due to complete 

 removal of the dermal fin rays. These results fall in line with 

 those described above for the unpaired fins. 



OPERCULUM. 



On January 15, 1906, a set of six fish had a piece of the 

 operculum removed, in order to determine whether the actual 

 bony structures of the fish would regenerate. The piece re- 

 moved was about one eighth of an inch broad and half an inch 

 long, and was taken from the lower posterior border. Six weeks 

 later two of these fish remained, but showed no signs of regen- 

 eration. A few days later, these also died. One fish with 

 operculum cut as above was kept in a dish in the laboratory for 

 four months, but at the end of this time showed no signs of re- 

 generation. 



The same experiment was tried with two sets of fifteen fish 

 each at Wood's Hole. These fish were kept from June 20, 

 1906, to August 25, 1906, but at the end of this period showed 

 no signs of regeneration. 



Fish operated on in the above manner are sometimes difficult 

 to keep alive since the gills are at first exposed to attacks of 

 parasites and the nibbling of other fish. In a short time, how- 

 ever, the branchiostegal membrane spreads over and partly closes 

 the opening. 



LOWER JAW. 



On March 23, 1906, pieces about one quarter of an inch long, 

 were removed from the right-hand side of the lower jaws of 

 thirty-six fish. Six weeks later, twenty-eight were still living. 

 The jaws had grown again to such an extent that some of them 

 could scarcely be distinguished from normal ones. Whether 

 new bone took the place of that removed, was not accurately 

 determined, though microscopic examination of sections of three 

 of these new structures seemed to indicate that cartilage at least 

 had regenerated. 



Attempts were also made to remove larger portions of the 

 jaw, or the entire jaw, but these always resulted in the death of 

 the fish even if the wound healed. This may have been due to 



