LANCELET, Amphioxvs or Braneltiostotna, a genus of dermopterous (q.v.) fishes, of very remarkable organization, far lower than that of any other vertebrate animals, con necting cartilaginous fishes both with mollusks and with annelids. A few species are known, all small; one of them (A. lanceolate's), the first which was discovered, a native of the coasts of Britain, and of-Europe generally. It inhabits banks of sand, and when dug up, buries itself again in the sand with wonderful activity. It is at the utmost scarcely more than 2 in, in length, very much compressed, tapering to a point at each extremity, the head not notably distinct from the body. It is silvery-white and semi transparent; the skin destitute of scales. A ]ow dorsal fin extends the whole length of the back. The skeleton is merely rudimentary, the spine being represented by a fibrouS sheath, containing a great number of transverse membraneous plates. There is no ves tige of a skull, or any enlargement of the spinal cord into a brain; nor is the lancelet furnished with organs of sight or of hearing. The mouth is situated beneath that put of the body which may be regarded as the head; and is surrounded by a cartilaginous ring, in several pieces. each of which gives off a prolongation to support elm, or short
filaments. The mouth communicates with a wide and long cavity, which contains the organs of respiration, and from the other extremity of which the alimentary canal pro ceeds. The lancelet does not eat or swallow, but simply imbibes its food, along with the water which supplies ail: for respiration. The intestine is slender and almost straight; but there is a very long cmcum. The walls of the respiratory cavity and the intestine are covered internally with vibratile cilia. The blood is colorless. Instead of a heart, there are several elongated blood-vessels, which contract successively; and at the commencement of each of the vessels connected with the organs of respiration there is a little contractile bulb. The muscular system accords with that of the higher fishes. —The very anomalous structure of the lancelet has led to the supposition that this genus may represent a family or order once more numerous, but belonging rather to former geologic periods than to the present.