REGENERATION OF FINS OF FUNDULUS HETEROCL1TUS. 397 



Here again it will be seen that the mean difference in reseller- 



o 



ation between S and M is over three times the probable difference, 

 in fact nearly six times ; the mean difference between S and L 

 shows that it is over nine times the probable difference so that 

 there can be no doubt that the shortest specimens in Table II. 

 regenerated at a more rapid rate than did the medium or the 

 longest. On comparing the medium with the longest we find that 

 the medium regenerated more rapidly than the longest as is evi- 

 denced by the fact that the mean difference is over five times the 

 probable difference. 



If we extend our hypothesis that there is a direct relation 

 between growth and regeneration further it would be to find out 

 whether as the fish grew older, the rate of regeneration decreased. 

 For this is precisely the condition as regards growth - - the rate of 

 growth decreases with age. At first the decrease is rapid but 

 then becomes very gradual. This is indicated with regard to 

 regeneration. For on comparing regeneration of the shortest 

 with the medium and the regeneration in the medium with the 

 longest we discover an indication of this relation. In each of the 

 two cases it is seen that mean difference in regeneration is greater 

 between shortest and medium as compared with the mean differ- 

 ence in regeneration between the medium and longest. 



It was said at the beginning of this section that in estimating 

 age we ought to consider both length and weight. So I have 

 placed opposite the length, etc., of each specimen its weight. A 

 priori, the youngest ought to be the shortest and lightest, etc. 

 This is the case here, for the average weight of the shortest is 

 3.38 gm.; the average weight of the medium length is 8.96 gm., 

 while that of the longest is 20.85 gm. So that in Table IV. our 

 three classes represent the youngest, the oldest and those midway 

 between the others in age. In the same way for Table V. the 

 average weight of the shortest is 4.48 gm.; that of the longest is 

 12.71 gm. while that of the medium length is 7.52 gm. In this 

 case also our three series in Table V. represent the youngest, the 

 oldest and the medium aged fishes of that lot. We conclude 

 therefore that the rate of regeneration in Fundnlus //. is greatest 

 in the youngest fishes, less in the older, and that there is a slight 

 indication that the rate of regeneration decreases with age. 



