2 THE TERIODIC GRO'WTII OF SCALES IN GADID^ 



years ago, suggested that I should endeavour to extend to marine fishes 

 this newly revived though really old hypothesis, that the age of certain 

 fislies might be determined by means of annual rings on their scales, 

 an hypothesis which Dr. Hofi'bauer had previously shown to be true 

 for some fresh-water fishes, such as the carp. To Dr. E. J. Allen I am 

 indebted, not only for placing all the possible facilities of the Plymouth 

 Laboratory at my disposal, but also for reading the manuscript and 

 proof-sheets. For the latter I am all the more indebted to Dr. Allen, 

 in that, as I WTite, I am just on the point of leaving this country to 

 take up a new biological appointment at Cape Town. I would further 

 express my obligations to Professor Mcintosh, Dr. T. Wemyss Fulton, 

 and Dr. H. M. Kyle, who generously lielped me in securing additional 

 specimens. I must add that without the aid of a Government Grant, 

 awarded through the Koyal Society, this work could not have been 

 accomplished in its present form. 



This paper consists of two parts : the first part contains a review of 

 the literature on fish- scales, more especially so far as that bears on the 

 subject of my investigation ; the second part is composed of statistics 

 dealing with the size, the number of growth-lines and annual rings in 

 scales from fish of all sizes, and captured at the various seasons of the 

 year. The accumulation of the necessary statistics for this second 

 portion of my work has been an arduous and lengthy task, involving, 

 as it has done, exact measurements of hundreds of scales and a more 

 superficial observation of thousands of others. 



II. Summary of Literature. 



I may firstly notice tliat, shortly after the invention of the microscope, 

 Borello wrote a brief description of the microscopic appearance of a fish 

 scale, and added a diagrammatic figure of the same.* 



About a hundred years later, Ilooke, in his Micrograpliia, gave a very brief 

 description, but a fairly exact figure, of the scales of the sole.f 



We are indebted to'Leuwenhoeck for several interesting notes on the de- 

 velopment and structure of scales. J In regard to the growth of scales, his 

 first idea was that each year the scales increased in size by adding a new zone 

 or circle to the pre-existing scale. Later, however, he abandoned this view, 

 as in examining certain scales lie observed that those of old fishes are very 

 thick, much thicker than they would necessarily be if their mode of increase 

 was simply by the addition of a new circle or zone each year. 



He came to the conclusion that the portion which he had at first taken for 

 a new zone disposed round the jn-imitive scale was simply the most external 

 ])art of a new scale, the part which exceeded tlie old scale in size, and that 

 all these scales were intimately welded together. 



* Borello, 1566. [For detailed references see Literature, p. 106.] 

 t Hcoke, 1667. X Leuwenhoeck, 1696. 



