104 THE TERIODIC GROWTH OF SCALES IN GADID^ 



monks, being therefore of great age. Sandeman has contributed a 

 paper to the Liunean Society showing that the eyes and other organs 

 show symptoms of senile decay. 



Lately, in the Field, it has been held that eels can breed in fresh 

 water. The lighthouse-keeper on the isle tells me that the eels found 

 by him are much smaller than those found formerly, that instead of 

 being five feet or so, they are only three feet or so in length. 



The scales of eels are well buried in the skin, and from this position 

 one would naturally suppose that they could not easily be shed or 

 rubbed off. The scales show rings very clearly ; but whether these 

 are annual or not I would not at present certainly determine, as I 

 have not a complete series of the fish. If the rings are annual, and 

 from the fact that these animals seem to have a winter sleep, it would 

 be natural to suppose that such is the case, then the eels on the Isle of 

 May are of no great age, and the largest of the specimens (35 inches 

 in length) examined by me, may not be more than fourteen years old, 

 but on this determination I do not place any exact reliance. 



The scales were thick, well preserved, and showed no signs of dis- 

 integration such as are found in scales from aged pollack. This may 

 be partly accounted for by the fact that scales in the eel do not over- 

 lap one another. 



IV. Conclusion. 



My present paper, firstly, rests on the foundation of Dr. Hoffbauer's 

 work for fresh-water fish, which no authority has as yet proved false. 

 Dr. Hoffbauer showed tliat scales gave a direct index of age in carp, 

 etc., for all of which he had exact and direct knowledge as to their 

 age and history. It is surely opposed to the principle of the unity 

 of science to believe that a law which holds true for some fresh-water 

 fish would not also be found applicable to some marine fish. 



After reading the preceding statistics, I think that it must be 

 granted that, even after allowing for variation, they afford strong 

 cumulative proof that in these species of Gadida the growth of scales 

 is cyclical or periodic, and that the rings formed thereby are annual. 

 To believe that these are not annual rings, but are rings formed in 

 some more irregular manner, seems quite opposed to the facts in regard 

 to the growth of the scale, and the arrangement of the lines which 

 mark that growth, as brought out by my statistics and plates. 



That scales of those Gadidre show a larger surface growth, and a 

 wider separation of the lines of growth in summer as contrasted with 

 winter, appears to me to be indisputable. This divergence in the growth 

 of scales during summer and winter is probably due to changes in the 

 general metabolism of the body, which are in their turn, in all proba- 



