12 C. V. MORRILL, JR. 



pointed knob in the middle of the old scar. The remaining 

 twelve were not kept after December 29 (twelve weeks after 

 operation). In all of these the regeneration was proceeding 

 rapidly at this time, some having the new fin half completed. 



On February 16, 1906, a second set of twenty-five fish had 

 the dorsal fin cut off close to the body. These regenerated more 

 rapidly than the first set and in five weeks' time, twenty-one of 

 these which still remained, were regenerating along the entire 

 length of the cut surface, in many cases the new growth being 

 one eighth of an inch in height. Three weeks later, fifteen only 

 were still living ; the increase in height of the fins was distinctly 

 visible in this short time, though more so in some individuals 

 than in others. Three weeks later (at the time of writing) and 

 twenty-three weeks after operation, fourteen were still alive. 

 The new fins in some cases were regenerating evenly and pos- 

 sessed the normal number of fin rays (eleven). But in other 

 cases, the new growth appeared along part of the cut surface 

 only. An examination of the anatomy of the fin and the exact 

 direction of the cut reveals the cause of this irregularity. Usu- 

 ally in trimming the fin close to the body, the dermal fin-rays 

 are severed a short distance distal to their articulation with the 

 bony supporting rays, beneath the surface. Sometimes, how- 

 ever, if the flesh at the sides of the fin is pressed down by the 

 scissors and the fin at the same time held firmly, the cut will 

 pass, in some places, through the enlarged proximal part of the 

 dermal fin rays and regeneration in consequence will be much 

 slower, or may not take place at all in parts so affected. The 

 cut may even at times remove the dermal rays completely. 

 These facts, I think, will account for cases in which regeneration 

 is irregular, i. e., when the new structure does not contain the 

 normal number of fin-rays. Thus complete or nearly complete 

 removal of the fin-rays prevents regeneration of the fin. 



ANAL FIN. 



The anal fins of eighteen fish were cut off close to the body 

 on October 25, 1905. The wounds healed up rather quickly 

 but showed no signs of regeneration until two months later, 

 when of the thirteen fish remaining, five showed slight signs of 



