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DEPARTMENT OF THE NAVAL SERVICE 



as will shortly be shown, this is,, in all probability, to be regarded as in connection 

 •with the fact that the lamellse themselves form a system of annual rings, which may 

 be rendered discernible by preparing the scales in a special manner. If we take, for 

 instance, fresh herring scales, treated, however, with nitric acid, and impregnate them 

 with bichromate of potassium, thereafter placing them in a solution of nitrate of 

 silver, a dark precipitate of some silver compound will be formed between the fibrils. 

 This precipitate is not amorphous, but is deposited in small spindle-shaped particles, 

 each with its axis in the direction of the fibrils, so that a preparation of this kind 

 distinctly shows the course of the fibrils themselves just as the course of currents 

 is shown on nautical maps. As the impregnation takes place only, or mainly, in 

 those layers which lie nearest the surface of the scale, it is possible, by gluing the 

 scale to be impregnated, on to a glass plate, to exclude one of its two surfaces from the 

 action of the silver solution and thus to impregnate either the innermost lamella? 

 alone, or only that portion of each, which lies immediately adjacent to the outer layer 

 of the scale. The operator can thus obtain at will either views as in fig. 12, giving 



Fig. 12. 



schematically a portion of the innermost lamellse, or as in plate IV, fig. 13, showing a 

 portion of a scale impregnated from the outer side. This latter shows, in another 

 manner, the same feature as seen in plate IV, fig. 6, while the former corresponds to 

 plate III, fig. 4. 



On examining a scale thus impregnated, with a low-power lens and in oblique 

 light, the small spindle shaped bodies will not be discernible. They produce, however, 

 by reflection an effect as shown in plate V, fig. 14. In this manner, an excellent view 

 is obtained as to the extent of the elementary lamellse, and it is at once strikingly 

 noticeable that the breadth of the zones exhibits an irregular progression, broader belts 

 suddenly appearing after a series of narrow zones. Closer comparison reveals the fact 

 that the transition from narrow to broader zones takes place just where the surface of 

 the scale shojvs a winter ring. Thus the elementary plates are seen to form their own 

 .system of annual rings, corresponding to that of the surface layer, but otherwise 

 differing' greatly from this, and more resembling that found in the scales of many 

 salmonoids and gadoids, etc, where the winter rings are not so sharply marked, but 

 a gradual transition from summer to winter is seen. 



The foregoing description as to structure of the scales does not apply to all the 

 scales found on the body"/ of a herring. On looking through a collection of herring 

 scales, some will be found to differ from the rest, being most easily distinguishable 

 from these by the fact that the zigzag boundary line between the two systems of stripes 

 (vide plate I, fi^g. 1) does not reach right down to the basal line, nnd that the stripes 

 in a more or less considerable central portion of the scale form irregular patterns, in 

 contrast to what is normally the case. Winter rings, again, are invariably lacking in 

 this abnormal central portion, although present outside it, excepting, of course, cases 



