67 



metallic lustre from the presence of numerous crystals of a 

 combination of guanin and lime. This 

 coating may readily be loosened and 

 rubbed off, and in one European fish, 

 the bleak or ablette, a member of the 

 carp family, the crystals are sufficiently 

 Crystals from the sii^^ery abundant to bccome the source of the 

 T^'TlLT""^'^' metallic pigment known in the arts as 



Magnified 600 times. i o 



Essence d' Orient or argentine, which is 

 used to impart a nacreous lustre to the glass globules sold 

 under the name of "Roman pearls." When the silvery coat- 

 ing is absent, scales are lustreless and transparent, as in the 

 smelt, the abdominal cavity of which, however, has a brilliant 

 silvery lining composed of the same substance. 



The colors of fishes are very varied and often exceedingly 

 brilliant and beautiful. "Aucune classe d' animaux n'a ete 

 aussi favorisee a cet egard," says Lacepede, "aucune n'a 

 regu une parure plus elegante, plus variee, plus riche : et que 

 ceux qui ont vu, par exemple, des zees, des chetodons, des 

 spares, nager pres de la surface d'une eau tranquille et 

 reflechir les rayons d'un soleil brillant, disent, si jamais 

 I'eclat des plumes du poeon et du colibri, la vivacite du 

 diamant, la splendeur de Tor, le reflet des pierres precieux, 

 ont ete meles a plus de feu, et ont renvoye a I'oeil de Tobser- 

 vateur des images plus parfaites de cet arc merveilleusement 

 colorie dont I'astre du jour fait souvent le plus bel ornament 

 des cieux." 



The colors are often due to a simple arrangement of pig- 

 ment cells, placed at different depths in the skin, but those 

 changeable and brilliant hues, which constitute the greatest 

 beauty of fishes, are dependent, as Pouchet and others have 

 shown, upon two very dissimilar causes. 



One of these, which may be well observed in the scales 

 of the herring, shad or mackerel, is a true iridescence, similar 

 to that seen in the pearl or in antique glass, and due to the 

 refraction of the rays of light as they glance off the surfaces 



