4. There is another aphya derived from fish, for that which is called cobitis is derived from small and inferior gobii, which bury themselves in the earth. The membrades are produced from the phalerica. The trichides come from these, and the trichiæ from the trichides; from one kind of aphya, which inhabits the port of Athens, the encrasicoli are derived. There is another kind of aphya which originates in the mœnis and cestreus, but the barren aphrus is very soft, and endures only for a short time, as I said before, and at last nothing is left but the head and eyes. The fishermen, however, have now found a mode of conveying it from place to place, for it lasts longer when salted. CHAPTER XV. 1. Eels are not produced from sexual intercourse, nor are they oviparous, nor have they ever been detected with semen or ova, nor when dissected do they appear to possess either seminal or uterine viscera; and this is the only kind of sanguineous animal which does not originate either in sexual intercourse or in ova. It is, however, manifest that this is the case, for, after rain, they have been reproduced in some marshy ponds, from which all the water was drawn and the mud cleaned out; but they are never produced in dry places nor in ponds that are always full, for they live upon and are nourished by rain water. It is plain, therefore, that they are not produced either from sexual intercourse or from ova. Some persons have thought that they were productive, because some eels have parasitical worms, and they thought that these became eels. 2. This, however, is not the case, but they originate in what are called the entrails of the earth, which are found spontaneously in mud and moist earth. They have been observed making their escape from them, and others have been found in them when cut up and dissected. These originate both in the sea and in rivers wherein putrid matter is abundant; in those places in the sea which are full of fuci, and near the banks of rivers and ponds, for in these places the heat causes much putridity. This is the mode of generation in eels. CHAPTER XVI.