64 Papers from the Marine Biological Laboratory at Tortugas. 



the cut to the free end of the fin. At first thought this statement seems only 

 a ditterent way of saying, " the greater the amount of injury the more rapid 

 will be the rate of regeneration." This is not true, however, as it was shown 

 that the rate of regeneration varied with the shape of the cut in a manner 

 not always correlated with the extent of the injury. Experiments will be 

 recorded in the present paper which seem to contrast the two factors dis- 

 tinctly, as well as to show the peculiar influence of the level at which the 

 cut is made. 



Again, Zeleny offers the interesting conjecture that the uninjured chelae 

 may be assumed to exert a retarding influence upon the growth or regenera- 

 tion of all the others. When one chela is removed the number of uninjured 

 limbs remaining is greater than when both chel?e and the last two pairs of 

 walking-legs are removed. The retarding influence with one chela gone, 

 if the supposition be true, is greater than it is when more limbs are removed 

 and correspondingly the rate of regeneration in the former is slower than 

 in the latter case. Such an explanation when modified might be applied to 

 regeneration in the salamander, the fish, and the medusa in the following 

 way : When these animals are cut at various levels they regenerate faster 

 the farther the cut surface, within certain limits of course, is from the ex- 

 tremity or limits of the animal's body. A fish's tail-fin grows faster from a 

 straight cut near the base than from a similar cut near the end of the fin. 

 The medusa regenerates tissue faster the farther away from the periphery 

 the cut is made, as though the more tissue removed the less uninjured body- 

 surface remained to exert a retarding influence. 



The above considerations suggest the question of the limits of growth ; 

 as the body nears its adult or normal size the rate of growth becomes slower. 

 It is also true that the regenerating tissue grows slower as it reaches the 

 limits of the former body-surface. Morgan ( 1006) has expressed this idea 

 as follows : 



If we can find the explanation for the cessation of growth at the proper terminus 

 we can probably find also an explanation for the difference in the rate at different 

 levels, for, as can be shown, the two things appear to be one and the same. In other 

 words, as the new part grows larger its materials change, and this change is of such 

 a kind that it leads to the cessation of growth. Hence starting under different con- 

 ditions at different levels the same end result will be reached in all cases, and when 

 the terniinas is reached the growth should slowly decline, as we find in fact that it does. 



Emmel (1906 and 1907) has arrived at opposite conclusions after a study 

 of regeneration and molting in the lobster from those cited above as ob- 

 tained by Zeleny on the crayfish. Scott (1907), from a study of regenera- 

 tion on the fins of Fniidiilus, reaches conclusions dift'ering both froin those 

 of Zeleny and Emmel as well, since he finds that the degree of injury exerts 

 no influence whatever over the rate of regeneration in the fish's fin. Be this 

 as it mav, the fact remains that in the salamander, the fish, the earthworm. 



