The manos is the one that grows to the largest size, but the softest of all are those found in the vicinity of Lycia. Where the sea is deep and calm, they are more particularly soft, while those which are found in the Hellespont are rough, and those in the vicinity of Malea coarse.[2745] When lying in places exposed to the sun, they become putrid: hence it is that those which are found in deep water are the best. While they are alive, they are of the same blackish colour that they are when saturated with water. They adhere to the rock not by one part only, nor yet by the whole body: and within them there are a number of empty tubes, generally four or five in number, by means of which, it is thought, they take their food. There are other tubes also, but these are closed at the upper extremity; and a sort of membrane is supposed to be spread beneath the roots by which they adhere. It is well known that sponges are very long-lived. The most inferior kind of all are those which are called “aplysiæ,”[2746] because it is impossible to clean them: these have large tubes, while the other parts of them are thick and coarse. CHAP. 70. (46.)—DOG-FISH.[2747] Vast numbers of dog-fish infest the seas in the vicinity of the sponges, to the great peril of those who dive for them. These persons say that a sort of dense cloud gradually thickens over their[2748] heads, bearing the resemblance of some kind of animal like a flat-fish,[2749] and that, pressing downward upon them, it prevents them from returning to the surface. It is for this reason that they carry stilettos with them,[2750] which are very sharp at the point, and attached to them by strings; for if they did not pierce the object with the help of these, it could not be got rid of. This, however, is entirely the result, in my opinion, of the darkness and their own fears; for no person has ever yet been able to find, among living creatures, the fish-cloud or the fish-fog, the name which they give to this enemy of theirs.