Page:Natural History, Fishes.djvu/226

212 are much coarser and less regular, often being interrupted, and seeming to run into each other, and frequently swelling into oval scars. This may, perhaps, be owing to the surface having been partially worn down by rubbing against the gravel of the bottom, or against other objects in the water. Besides the concentric lines, there are seen on many of the scales, especially those of the lateral line, radiating lines varying in number from one to twenty or more, diverging from the centre towards the circumference, and frequently connected by cross lines forming a sort of network around the centre, (see c). Under the microscope these lines appear to be elevated ridges, dividing the concentric lines; but of their use we are ignorant.

In the microscopical examinations which we instituted while writing these pages, we ascertained some interesting facts. The brilliant golden or silvery reflection that constitutes the beauty of these lovely fishes depends not on the scales themselves, but on a soft layer of pigment spread over their inner surface, and seen through their translucent substance. On carefully detaching a scale, we see on the under side, opposite to that portion only which was exposed, all the concealed parts being colourless, a layer of soft gleaming substance, easily separable, either silvery or golden, according to the hue of the fish. If now we remove a small portion of this substance with a fine needle, and spread it on a plate of thin glass, we shall find, by the aid of the microscope, that it consists of two distinct substances; the one giving the colour, the other the metallic lustre. With a power of 300