This order, though composed of minute forms, is one of great economic importance, from the fact that the little crustaceans exist in vast numbers and furnish a very considerable part of the food of many fishes. ^Cyclops^ is the most common of the fresh-water, and ^Cetochilus^ of the marine genera. These, together with other genera, swarm in water wherever life exists, from the smallest pools and ditches to the broad surface of the ocean. Without having drawn a surface-net on some sheltered bay, it is difficult to have an idea of the myriads of /Entomostraca/ in the sea. Although nearly transparent and of such delicate texture as to be almost jelly-like, they sometimes color the sea with a reddish tint for miles. Whales which have baleen, or fringes of whalebone, in the mouth subsist on these small organisms, which are called "brit" by the whalemen. The whales, sometimes in schools, rush through the water with open mouths, engulfing these little [pg250] crustaceans, the baleen straining them from the water. Although devoured in such immense quantities, and sometimes lying dead in sheets of scum on the surface of the water, they maintain their numbers by the exceeding rapidity with which they reproduce. It has been computed that the descendants of one /Cyclops/ may number in one year 4,500,000,000, provided all the young reach maturity and produce a full number of offspring. One of the free marine forms, ^Sapphirina^, is of especial interest, as it surpasses all animals in phosphorescence and sparkles by day as well as by night. It is one quarter of an inch long, and is broad and flat. Besides the myriads of free-swimming copepods, there are parasitic forms in great number. The marine parasitic forms are commonly known as fish-lice. They have various habits, some living as commensals, others attaching themselves to animals only to be carried about; the true parasites live upon the blood and tissues of their hosts, and may fasten themselves to the external parts of the body or to the internal organs. Whales, fishes of all kinds, mollusks, starfishes, jellyfishes, and corals, all have some form of parasite, and many have several different kinds of guests. It is said that the haddock has more than a dozen which infest its external and internal membranes. ^Nicothoë^ is found on the gills of lobsters. The truly parasitic forms are usually very degenerate and lose the characteristics of their order. ORDER =CIRRIPEDIA= ("/Curled feet/") THE BARNACLES