ANNUAL RINGS IN SCALES. 471 
The second part will deal with experiments which were performed with 
a view to solving the problem of what are the conditions necessary to 
the production of these annual rings. 
PART £ 
METHODS. 
A very few observations were sufficient to convince me that it was 
impossible to detect with any certainty rings on the scales of either 
Flounders or Plaice by the ordinary methods of examination. The 
sclerites, that is the thickened cells covering the scale, were apparently 
of such a uniform width that it was almost impossible to differentiate 
between the wide ones formed in the summer and the narrow winter ones. 
In 1915 Winge published a paper on the scales of the cod, and described 
a new method which he had employed for his investigation. 
His method was as follows: ‘‘ A microscope stand with mechanical 
stage and ocular micrometer, and an objective having a focal diameter 
of about 8 mm. form the best combination. . . . One or more scales— 
fresh scales are especially suitable on account of their transparency—are 
placed on the object glass, their longitudinal axis about parallel with the 
longitudinal direction of the object glass itself. The micrometer is turned 
so as to fall parallel with the scales. . . . In order to obtain a curve for 
one of the scales the instrument is focussed to the centre of the one 
selected, and all sclerites in the longest radius of the scales then measured. 
. . . In order to provide a survey of the values thus obtained, the units 
are noted down on square-ruled paper. A horizontal axis is drawn, from 
which the measurements of the calcareous plates are marked off in a 
perpendicular direction, one by one, against each perpendicular line on 
the paper. On joining up the points thus obtained by straight lines, a 
curve is produced, which gives a distinct view of the variations in the 
breadth of the sclerite rings from the centre of the scale towards its 
periphery. Where the curve is low, the sclerites have been small, where 
it lies high, they have been large. A glance at the horizontal axis will 
show how many sclerites in all the scale contains, as also the number 
situate between each minimum, and the next. The growth rings are 
thus shown graphically as an alternation of maxima and minima.” 
The method given above is broadly the one which I employed in my 
investigations. The scales were examined in fresh water. The propor- 
tional width of successive sclerites is obviously the important factor to 
determine, thus making the absolute width of each sclerite of little 
importance. I used the distance between two degrees marked on the 
micrometer as the unit, each division being 10 u. 
