Structure of the Scales of Fishes. 2'^'J^ 



different forms of these lines, and the modifications they undergo in the 

 series of scales, but have likewise illustrated the functions which thej^ 

 probably perform in the organization of the latter. 



These longitudinal lines undergo every degree of formation, from that 

 of a perfectly closed canal, to that of a simple furrow. We shall some- 

 times see them present the form of a canal pierced on its upper side, per- 

 mitting a view of the thickness of the walls so pierced, as well as the bot- 

 tom ; sometimes these same lines Avill appear in the form of canals with 

 the whole of the upper wall removed ; sometimes they are merely fur- 

 rows, placed in the upper layer of tlie scale, and having the lower bed of 

 this tissue as a base. In certain cases we perceive them traversing the 

 osseous scale singly ; at other times they anastomose with each other, 

 and scales are to be found on which they form spines. We shall now 

 proceed to study these forms in detail. 



;. If we examine the scales of Acerina vulgaris — (pi. III. fig. 4) — it will be 

 seen that the longitudinal lines appear as canals alternately contracted and 

 dilated. The contracted parts present nothing but a rounded body; and 

 nothing throws light either on its nature or structure. We should remain 

 in uncertainty, if the dilated parts, which are a continuation of the same 

 lines, did not assist us in discovering their organization. The dilated 

 parts evidentl}' shew that the upper wall is partly removed ; we then see 

 not only the bottom of the canal — (fig 4, «,) — which is sometimes granu- 

 lar, at other times presenting transverse strira ; but wc can generally, 

 likewise, distinctl}' perceive the thickness of the wall indicated. It is 

 bordered by a double line (fig. 4, b), one of which belongs to the opening. 

 Cases also exist in which the opening is indicated only by a simple edge. 

 These different forms may be explained by the different degrees of incli- 

 nation in which the upper wall has been removed ; sometimes, in fact, it 

 is merely grazed, while at other times it is more or less deeply cut. 



If we now proceed to examine a scale of MuUus harbatus (pi. III. fig. 5), 

 we shall still perceive longitudinal lines closed at intervals ; but the up- 

 per wall is removed in considerable portions, and the bottom of the canal 

 easily- seen. These are, therefore, hollow tubes, the upper wall of 

 which is wanting throughout the greater part of their course. The 

 bottom is placed on the under laj^er of the scale, and the lateral walls 

 are formed by the upper layer. The engraving sufficiently shews, that 

 the cellular lines are never continued into the closed canals, neither in 

 llic latter case, nor in the scale formerly described. 



The scale of Serranus (pi. III. fig. G), presents in its longitudinal lines 

 hollow tubes, of which a part of the upper wall is entirely wanting. Wc 

 perceive from the engraving that the canal is nowhere closed ; but it is 

 casj- to distinguish the bottom as well as tlie lateral walls, which are 

 covered with granulations, of which we will afterwards find an explana- 

 tion. The longitudinal line, in this instance, still .approaches more or 

 less to the rounded form of a canal ; it is an intermediate stage betweeii' ' 

 a canal and a furrow. ''''■ '-"'''' 3" 



Lastly, if wc examine a scale olPercarina Dcmidoffii (pi. III. fig. 7)j and 



