Bibliographical Notices, 6S but we also find, as a peculiar plisenomenon, the migration of marine Fishes up the streams, in order to spawn, and, more rarely, that of river Fishes into the sea for the same purpose (the Eel ; see Spallanzani's observations in Commachio, G. von Martens' Italien, ii. p. 334). Here therefore they are even the same individuals which alternately inhabit the two media ; and perhaps this is not all, for it is said of several lakes that fishes which have immigrated into them from the sea are unable to find their way back, in consequence of the deficiency of current, and that they remain, as well as their posterity, in the fresh water; and on the other hand, Nilsson in his Scandinavian Fauna, in referring to our Shad (Alosa), does not say a word about its ascending into the fresh water, but, on the contrary, states that, according to the observations of Malm, it spawns between the rocky shelves of Gothenburg (Gotheborg's skargard). Marine Mammalia also sometimes ascend the rivers, but with less regularity, and principally following the migratory Fishes, as was observed by Simpson* to be the case with Seals in the Oregon river as far as the rapids of Les Petites Dalles. Whether the common Seal which, according to E. Bollf, was killed in the Elbe near Dessau, is to be referred to this category, or whether it was one that had escaped from human custody, remains doubtful as a single case at such a distance from the sea. The great richness of the sea is explained not only by its greater extent, but also by its more uniform temperature. The fresh waters stand in the same relation to it, as a continental to an insular climate ; their alternation of temperature is the prin-cipal hindrance to their becoming populous, and this attains its maximum by freezing in the colder zones ; with the increase of temperature the populousness of the fresh waters increases, but is still limited in the subtropical zone by partial desiccation. In the tropical zone, the conditions of temperature of the fresh waters approach most nearly to those of the sea, and with them their populousness. BIBLIOGRAPHICAL NOTICES. The Natural History of the Tineina, By H. T. Stainton, assisted by Prof. Zeller and J. W. Douglas. Vol. II. 8vo. London : Van Voorst, 1857. After an interval of nearly two years, we have to call the attention of our readers to the appearance of a second volume of this highly * Narrative of a Journey round the World, 1841-42. t Archiv des Vereins fur Naturkunde in Mecklenburg, 10 Heft, 1856, p. 73,
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