Certain animals are produced only at certain seasons of the year, both in water and on the land, such, for instance, as scallops, snails, and leeches, in the spring, which also disappear at stated periods. Among fishes, the wolf-fish[2789] and the trichias[2790] bring forth twice in the year, as also do all kinds of rock-fish; the mullet and the chalcis[2791] thrice in the year, the cyprinus[2792] six times, the scorpæna[2793] twice, and the sargus in spring and autumn. Among the flat-fish, the squatina brings forth twice a year, being the only[2794] one that does so at the setting of the[2795] Vergiliæ in autumn. Most fish spawn in the three months of April, May, and June. The salpa brings forth in the autumn, the sargus, the torpedo, and the squalus[2796] about the time of the autumnal equinox. The soft fishes[2797] bring forth in spring, the sæpia every month in the year; its eggs adhere together with a kind of black glutinous substance, in appearance like a bunch of grapes, and the male is very careful to go among them and breathe[2798] upon them, as otherwise they would be barren. The polypi couple in winter, and produce eggs in the spring twisted in spiral clusters, in a similar manner to the tendrils of the vine; and so remarkably prolific are they, that when the animal is killed in a state of pregnancy, the cavities of the head are quite unable to contain the multitude[2799] of eggs enclosed therein. They bring forth these eggs at the fiftieth day, but in consequence of the vast number of them, great multitudes perish. Cray-fish, and other sea-animals with a thinner crust, lay their eggs one upon the other, and then sit upon them. The female polypus sometimes sits upon its eggs, and at other times closes the entrance of its retreat by spreading out its feelers, interlaced like a net. The sæpia brings forth on dry land, among reeds or such sea-weed as it may find growing there, and hatches its eggs on the fifteenth day. The loligo produces its eggs out at sea, clustered together like those of the sæpia. The purple,[2800] the murex, and other fishes of the same kind, bring forth in the spring. Sea-urchins have their eggs at full moon during the winter; sea-snails[2801] also are produced during the winter season. CHAP. 75.—FISHES WHICH ARE BOTH OVIPAROUS AND VIVIPAROUS.