These fish are caught in various ways, but particularly in osier pots or baskets formed to entrap them, and also in nets. In some parts of the country they are boiled, and afterwards packed into barrels with vinegar and spices. 255. _The LESSER LAMPREY_ (Petromyzon fluviatilis) _is a fresh-water fish, distinguishable from the true lamprey by its much smaller size, the second dorsal fin being angular and connected with the caudal fin, and having a single row of teeth placed circularly in the mouth._ _This fish seldom exceeds the length of eight or ten inches._ _It is found in the rivers of most parts of Europe, America, and Asia; and particularly in those of Brandenburgh, Pomerania, Silesia, and Prussia._ In the spring of the year these fish are frequently seen sticking, by their mouth, to stones in shallow water, from which they may easily be taken with the hand. They are considered a very delicious fish for the table, in whatever way they are cooked. The best season for them is betwixt the months of December and April. Great numbers of Lesser Lampreys are caught in the Severn, the Dee, and the Thames; but particularly in the latter, near Mortlake in Surrey. Anterior to the late war more than 400,000 of them were annually sold to the Dutch as bait for cod, turbot, and other large fish. ---- CLASS V.--INSECTS. ---- 256. _The SPANISH FLY, or BLISTERING LYTTA_ (Lytta vesicatoria), _is a coleopterous insect (12), about an inch in length, of shining blue-green colour with black antennæ._ _It is found in most parts of Europe, and feeds on the leaves of the ash, poplar, elder, lilac, and other trees._ These insects, which are known in medicine by the name of _cantharides_, are of incalculable importance to mankind, as the basis of blistering plasters, and also as an internal remedy against many diseases. We import them in a dried state, from Spain, Italy, and the South of France; in many parts of which countries, about the middle of summer, they are found in vast abundance. As they are generally in a torpid state during the day, they are easily collected, by shaking them from the trees upon a cloth spread on the ground to receive them. When a sufficient number has been collected they are tied in bags, and killed by being held over the fumes of hot vinegar. After this they are dried in the sun, and packed in boxes for sale. The odour which is emitted by these insects is peculiarly nauseous, and so powerful, that great injury has sometimes been experienced by persons employed in picking them, and by those who have even fallen asleep under the trees where they abound. Previously to being used they are pounded; and if, in this state, they be applied to the skin, they first cause inflammation, and afterwards raise a blister. The usual blistering plaster is formed with Venice turpentine, yellow wax, Spanish flies, and powdered mustard.