Another remarkable feature of the abyssal waters of the Mediterranean consists in their poverty of animal life. No doubt there is some life; the dredgings of the _Porcupine_ and the telegraph cables, which, on being brought to the surface, were found to be covered with shells and polypes, prove this. But, compared with those of the ocean, the depths of the Mediterranean are veritable deserts. Edward Forbes, who explored the waters of the Archipelago, arrived at the conclusion that their abyssal depths were entirely devoid of life, but he was wrong when he assumed an exceptional case like this to represent a universal law. Carpenter thinks that this absence of life in the depths of the Mediterranean is due to the great quantity of organic remains which is carried into it by the rivers. These remains absorb the oxygen of the water, and part with their carbonic acid, which is detrimental to {29} animal life. In numerous instances the water of the Mediterranean contains only one-fourth the normal quantity of the former gas, but fifty per cent. in excess of the latter. To the presence of these organic remains the Mediterranean is probably indebted for its beautiful azure colour, so different from the black waters of most oceans. This blue, then, which is justly celebrated by poets, would thus be caused by the impurity of the water. M. Delesse has shown that the bottom of nearly the whole of the Mediterranean is covered with ooze. The regions of the Mediterranean immediately below the surface abound in animal life, particularly on the coasts of Sicily and Southern Italy; but nearly all species, whether fish, testacea, or others, are of Atlantic origin. The Mediterranean, in spite of its vast extent, as far as its fauna is concerned, is nothing but a gulf of the Lusitanian Ocean. Its longitudinal extension and the similarity of climate in its various portions have favoured the migration of animals through the Strait of Gibraltar as far as the coasts of Syria. At the same time, animal life is most varied near this point of entry, and the species met with in the western basin are generally of greater size than those which exist in the eastern. A very small proportion of non-Atlantic species recalls the fact that the Mediterranean formerly communicated with the Red Sea and the Indian Ocean. But amongst a total of more than eight hundred molluscs there are only about thirty which have reached the seas of Greece and Sicily through the ancient straits separating Africa from Asia, instead of through the Strait of Gibraltar.[9] The diminution in the number of species in an easterly direction becomes most striking when we reach the narrow channel of the Dardanelles and the Bosphorus. The Black Sea, in fact, differs essentially from the Mediterranean proper as regards temperature. It is refrigerated by north-easterly winds sweeping over its surface, to the extent even of portions of it becoming now and then covered with a thin coating of