After about eighteen weeks the eggs begin to hatch, and the fry wriggle out of the nest and seek shelter under stones in the immediate neighbourhood. They are now peculiar little creatures, as much like tadpoles as fishes, with big heads and narrow bodies, and a bag of albuminous yolk-matter attached to the ventral side. The young subsist on this store of food for from twelve to twenty days, during the whole of which time they remain under shelter, having, of course, no need to expose themselves to the numerous enemies with which they are surrounded, and they then leave their hiding-place in search of food, being now about an inch in length. They feed on aquatic and other insects, which are now becoming plentiful on the approach of the warm weather; and, growing rapidly, reach a length of four inches in a month or two. They are now called _parr_, and are distinguished by the dark bars that cross their bodies transversely--a feature that persists for a year or more from this time. Towards the end of May the parr migrate seawards, accompanied by the adult salmon, but as their enemies include the voracious fishes, wading birds, and even the adults of their own species, it is probable that only a small proportion of the original number ever enter salt water. In the sea they feed on crustaceans, molluscs, and small fishes, the young still growing rapidly, and attaining a weight of about five pounds in the following autumn, when both young (now called _grilse_) and old again ascend the rivers to spend the colder half of the year; the former will have reached a weight of ten pounds or more on their return to the sea in the following year. The Smelt may be seen in thousands in our estuaries during the spring, for at that time they come up to spawn in the brackish water. In the summer they swim about in shoals along the coast, and are caught largely in nets for the market. In some parts they are taken in large shallow circular nets suspended on a line. This is lowered into the water, and hauled up when the fish are seen swimming above it. Many amateurs secure numbers of smelt by means of rod and line, fishing from piers, jetties, &c. They bite freely at almost any kind of bait, and will snap at an almost bare hook, with the tiniest fragment of the bait at its point. The Herring family (_Clupeidæ_) contains some well-known food-fishes to which we need only casually refer. They are mostly littoral species, none inhabiting deep water, and none straying into the open ocean. Their bodies are covered with silvery scales, and are laterally compressed, so much so on the ventral side that there is a moderately sharp ridge along the middle line. The principal fishes of the family are the Herring (_Clupea harengus_), the Sprat (_C. sprattus_), and the Pilchard (_C. pilchardus_).