The true nature of the spouting of a cetacean seems to be very generally misunderstood, the fountain of spray produced at each exhalation giving the idea that the animal is expelling a quantity of water from its nostrils. This, of course, is not the case; for the cetacean, being an air-breather, has no need to take in a supply of water, as the gill-breathing fishes have. Air only is expelled through the nostrils; but as the expiration sometimes commences before these apertures are brought quite to the surface, a certain amount of water is shot upwards with the expired air; and even if the expiration commences after the nostrils are exposed, the small quantity of water they contain is blown into a jet of spray; and in a cool atmosphere, the density of this is increased by the condensation of vapour contained in the warm and saturated air from the lungs of the animal. It will be noticed, too, that the creature does not check its course in the least for the purpose of respiration, the foul air being expelled and a fresh supply taken in exchange during the short time that the blow-hole remains above the surface of the water. The Common Porpoise measures five or six feet in length, and subsists on pilchards, herrings, mackerel, and other fish, the shoals or ‘schools’ of which it pursues so closely that it is often taken in the fishermen’s nets. Its flesh was formerly eaten in our own country, but it is now seldom hunted except for its oil and its hide. About three or four gallons of the former may be obtained from each animal; and the latter is highly valued on account of its durability, though it should be known that much of the so-called porpoise-hide manufactured is really the product of the White Whale. CHAPTER XV _SEA WEEDS_ We now pass from the animal to the vegetable kingdom, our object being to give a general outline of the nature and distribution of the principal marine algæ or sea weeds that grow on our shores; and to supply a brief account of those flowering plants that either exhibit a partiality for the neighbourhood of the sea, or that grow exclusively on the rocks and cliffs of the coast. The present chapter will be devoted to the sea weeds themselves, but we consider it advisable to precede our account of these beautiful and interesting plants by a brief outline of the general classification of plant-life, in order that the reader may be able to understand the true position of both these and the flowering plants in the scale of vegetable life.