No. 378. ] ARTIFICIALLY HATCHED FISH. 4II 
are to be taken. After the “planted fish” have had time to 
mature, new curves should be plotted for the first locality. If 
these curves are practically the same as those originally made, 
it is reasonable to conclude that the re-stocking has been inef- 
fectual. If, however, the new curve approaches the curve of 
the locality from which the “brood fish” were taken, it is 
reasonable to conclude that the influence of the foreign speci- 
mens has been felt, and the re-stocking has been effectual. 
The following objections may be raised to the above method : 
(1) It may be that, due to the small number of specimens 
(100), the curve A is not characteristic of the Woods Holl speci- 
mens, and its difference from curve B is only accidental. To 
test this source of possible error I have examined three separate 
groups of flatfish, all from the same locality, each group contain- 
ing 100 specimens. The resulting curves are strikingly alike. 
Of course it would be much more satisfactory to base all the 
curves on the enumeration of the fin-rays of one thousand rather 
than one hundred specimens, but even one hundred specimens 
yield fairly definite results, though the curves are somewhat 
uneven, 
(2) It may be that the variation in the position of the curves 
is a result of age, z.e., the fishes from Woods Holl averaged 
a larger number of fin-rays because they were somewhat older. 
If there is an increase in the number of fin-rays on the part 
of the older specimens, this increase can be readily detected by 
simply comparing the average number of fin-rays of the younger 
with the average number of fin-rays of the older fish. Fifty- 
three young fishes, less than 10 inches in length, have a mathe- 
matical average of 66.1 dorsal fin-rays. Forty-seven older 
fishes from the same locality, all over 10 inches in length, 
average practically the same number of fin-rays, se, 66.3. In 
this collection of 100 fishes, the fourteen smallest have a greater 
average number of fin-rays than the fourteen largest. There is 
then no material increase in the number of fin-rays with 
increase in age. 
(3) It may be that the variations tabulated in Fig. 1 are the 
result of environmental conditions expressed upon the fry and 
young — acquired characters of questionable hereditary value ; 
