C.\\.\rn\\ FISflFRfF.^ F.Xrr.DITloy, 101 'r15 



89 



an intense blue colour, while all the remainder is unaffected.^ Sections show that 

 this upper covering layer is of almost equal thickness at the edge and near the centre 

 of the scale, and evidently does not grow thicker; it is thus easy to understand that the 

 winter rirbg-s, for instance, upon the surface of this layer, continue eiiually distinct 

 many years after formation, in contrast to what is found be to the case witli otoliths, 

 where the earliest annual rings become entirely concealed, and are only discernible 

 after the otolith has been ground down so as to expose its inner structure. 



An examination of sections also reveals a number of breaks in the upper layer; 

 these will be found to be the so-called radial furrows {vide plate I, fig. 1), which run like 

 channels in the surface layer. Finally, it will be seen that the exterior covering layer 

 extends out beyond the edge of the fibrillar plates and forms by itself, independently 

 of these, the margin of the scale. The winter rings are not particularly conspicuous 

 in a section ; despite the most careful orientation by means of the fine ridges on the 

 surface, it has not been found possible to discern any conspicuous peculiarity in those 

 parts of the outer layer where the winter rings lie. It is noticeable that the ridges, 

 which resemble the teeth of a saw, are set somewhat irregularly; possibly, also, the 

 outer layer itself is slightly thinner in the inner than on the outer side of the point 

 where a winter ring is situated. These features are, however, so inconspicuous, that 

 without exact orientation it would be impossible to demonstrate where the winter 

 rings actually lie in a section. Figs. 9 to 11 give diagrams of various details from 

 sections of herring scales. 



Fig. 9. 



Fig. 10. 



'rr^^^TTf^^^^r^^ 



Fig. 11. 



Below the (juter ccnering layer may be seen, viewing the scale in section, a 

 thicker stratum, divided into zones of varying appearance. If the section be embedded 

 in a medium of low refraction, it may be distinctly seen that the fibrils in some of the 

 zones have been cut transversely across, whereas other zones are clearer, with less 

 apparent structure, suggesting that the fibrils here are not transversely severed. This 

 layer formaticm may be strikingly shown ])y placing the sections in polarized light, 

 when, in certain positions, a series of bright bands, with darker zones between, will b" 

 apparent. It will then be distinctly seen that the thickness of the lamella? varies, and, 



1 This staining did not succeed, when the scales cut had been treated with acids in order to 

 remove inorganic matter. I have, by microchemical reactions, satisfied myself of the fact that 

 practically all inorganic matter (principally phosphate of lime) is in the herring scales deposited 

 in the outer covering layer, while the fibrillar plates are devoid of it. I suspect that the 

 differential staining is due to the presence of metallic salts in the one layer only, the salts acting, 

 as it were, as a mordant. 



fi551— 10 



