The young Barnacle when just extruded from the shell of its parent is a very different being from that which it will be in its mature condition. It begins its life in a form exactly like that of an entomostracous crustacean, and, like a Cyclops, has one large eye in the middle of its forehead. In this state it swims freely, and with great activity. It undergoes three moults, each time altering its figure, until at the third exuviation it has become enclosed in a bivalve shell, and has acquired a second eye. It is now ready to attach itself to its abiding-place; so, selecting its future residence, it presses itself against the wood, or whatever the substance may be, pours out from its two antennae a glutinous cement, which hardens in water, and thus fastens itself by the front of its head, is henceforth a fixture for life, and assumes the adult form in which most persons know it best.[97] [97] If any of my readers wish to observe the development of young barnacles they may easily do so. The method I have generally adopted has been as follows: Procure a shallow glass or earthenware milk-pan that will hold at least a gallon. Fill this to within an inch of the top with sea-water, and place it in any shaded part of a room--not in front of a window. Put in the pan six or eight pebbles or clean shells of equal height, say 1-1/2 or 2 inches, and on them lay a clean sheet of glass, which, by resting on the pebbles, is brought to within about 2-1/2 inches of the surface of the water. Select some limpets or mussels having acorn-barnacles on them; carefully cut out the limpet or mussel, and clean nicely the interior of the shell; then place a dozen or more of these shells on the sheet of glass, and the barnacles upon them will be within convenient reach of any observation with a magnifying glass. If this be done in the month of March, the experimenter will not have to wait long before he sees young _Balani_ ejected from the summits of some of the shells. Up to the moment of their birth each of them is enclosed in a little cocoon or case, in shape like a canary-seed, and most of them are tossed into the world whilst still enclosed in this. In a few seconds this casing is ruptured longitudinally, apparently by the struggles of its inmate, which escapes at one end, like a butterfly emerging from its chrysalis, and swims freely to the surface of the water, leaving the split cocoon or case at the bottom of the pan. Some few of the young barnacles seem to be freed from the cocoon before, or at the moment of, extrusion. From three to a dozen or more of these escape with each protrusion of the cirri of the parent, and as the parturient barnacle will put forth its feathery casting net at least twenty times in a minute for an hour or more, it follows that as many as ten thousand young ones may be produced in an hour. These, as they are cast forth at each pulsation of the parent's cirri, fall upon