It v;a5 found that pilchard scales appear to excellent advantage 

 and the surface structure is brought out in bold relief in a medium of 

 air. Accordingly, the specimens were mounted dry, — 6 or 8 for each fish,- 

 between two glass slides stuck together at the ends with glue and clamped 

 together tightly, until the latter dried, so as to flatten the scales 

 and insure their remaining in place. £/ To mount scales from 100 fish 

 required about 6 hours . 



The specimens thus prepared were examined with the aid of a project- 

 ing microscope so arranged that the projected image appeared on the table 

 beside the microscope. It is the impression of the authors, perhaps 

 purely personal, but probably not, that the year marks appear much more 

 clearly in the projected image than when viewed directly tlirough the 

 microscope. 



For each specimen a punch card designed for the ready tabulating 

 and sorting of data was laid on to the image so that a millimeter ruler 

 printed on the card extended along the mid-longitudinal axis of the 

 sculptured part of the scale, its zero line coinciding with the base 

 of the latter. Lines were then drawn through the ruler where the lat- 

 ter was crossed by "annuli." Subsequently there were recorded on the 

 card such pertinent data as sample number, length of fish, locality and 

 date of collection, dimensions of scale and position of marks, etc. 

 Thus a permanent quantitative record was obtained for every examination. 



To learn the characteristics of an annual mark, scales of young 

 pilchards were examined over the course of a year. A concentric mark 

 was observed to have formed consistently by early spring. As a result 

 of these preliminary examinations, vre recognized as annuli those marks 

 having the following characteristics t 



An annulus is concentric with the margin of the scale. It 

 is not, always a sharp or unbroken line; nor are the segments 

 of an interrupted annulus alvfays perfectly cocircular (if the 

 shape of a scale may be called circular in this discussion). 

 But the course of an annulus, continuous or broken as it may 

 be, can usually be traced, by careful scrutiny if necessary, 

 entirely around the sculptured part of the scale from left- 

 hand to right-hand margins. Sometimes they can even be fol- 

 lowed around the unsculptured part. Annuli are clearly sepa- 

 rated from each other and do not ordinarily meet at any point. 

 If an annulus has formed, it is present in all the normal scales 

 of an individual . ' ~ 



Tt'e have recognized as adventitious, or otherwise unperiodic ("false 

 rings") those marks distinguished by the following characteristics: 



-AiThile this paper was in manuscript, a publication by Aikawa (19U0) 

 was received. It de'^cribes the same mounting technique as that used 

 in our study. 



39 



