Page:Natural History, Fishes.djvu/145

Rh still; as they are said to appear among the Orkney Islands, and in the Frith of Forth about the end of July or the beginning of August.

It is now generally believed that the whole of the phenomena of the seasonal appearance and disappearance of fishes may be accounted for on the principle, now pretty well ascertained, that the vivification of the spawn requires its deposition in situations where the sun's rays can have ready access to it. But this would be impossible if it were deposited on the bottom in considerable depths of water; and hence, these animals have been endowed with instincts, which impel them at the proper period, to resort to the shallows of the coast, where the incumbent stratum of water is not too great to allow the solar light and heat to penetrate to the sand and gravel of the bottom, among which the ova are to find their resting-place.

On this interesting subject we are glad to quote the opinions of one of the most illustrious of ichthyologists. "It does not appear," observes Mr. Yarrell, "to have been sufficiently considered, that, inhabiting a medium, which varied but little either in its temperature or productions, locally,—fishes are removed beyond the influence of the two principal causes which make a temporary change of situation necessary. Independently of the difficulty of tracing the course pursued through so vast an expanse of water, the order of the appearance of the fish at different places on the shores of the temperate and southern parts of Europe is the reverse of that which, according to the theory [of the older naturalists], ought to have happened. It is known that this