Il4 Dr L. Mandl om the Scales of Fishes. 



formed every year below tlie old one, wliicli forms a margin 

 round it, so that we perceive on the scale the margin of the 

 old scale ; and that we may, in this manner, by counting the 

 number of layers in a transverse section, determine the age of 

 the fish, and tlie number of accessory scales which compose 

 the entire scale. We shall afterwards point out the errone- 

 ousness of this opinion, merely remarking for the present, 

 that the drawing which Leuwenhoek gives for a transverse 

 section, represents nothing more than a part of the surface, 

 and by no means the interior of the scale. This author had 

 previously started another opinion (Arc. Nat. (Op. omnia, t. 

 1) Lugd. Batav. 1722, p. 105, 1685), the discovery of the 

 scales of eels, of which he has furnished a better figure than 

 any of his successors (Opera omnia, t. i. p. 48) and which he 

 believed composed of globules ; and some investigations relating 

 to the perch, had led him to believe that a scale grows like 

 wood, that is to say, that it forms a new circle every year. 

 This opinion he subsequently abandoned, as we have just seen. 

 Reaumur (History of the Academy, 1716, Paris, 1718, 

 p. 229) had already remarked that the silvery substance observed 

 by the microscope or a powerful glass, is composed " of plates, 

 the greater part of which are cut in a square form. These 

 plates form rectangles about four times longer than broad ; 

 some of them, however, have their extremities rounded, and 

 others terminate in points. They are all extremely thin." 

 This author believed that these crystals could not be broken, 

 an error ai'ising from the circumstance of his having taken 

 fragments for entire crystals. He affirms that these ci'ystals 

 are contained in vessels or a kind of tubes, mistaking the 

 bundles in which they are naturally disposed for vessels. 

 Reaumur believes, moreover, that the formation and growth 

 of the scales of fishes is owing to this matter. If the essence 

 (V Orient becomes putrid during summer, it is, he assures us, 

 on account of the animal parts accidentally found there in so- 

 lution, the crystals, according to him, being unalterable. This 

 latter observation has not been confirmed by our researches. 

 He also gives us a detailed description of the manner in 

 which false pearls are formed by means of this matter, the 

 presence of which on the lower side of the scale he very dis- 



