LANCELET(Branchiostoma [or Amphioxus ∖ lanceolatum). This creature, the lowest in the scale of fishes, with which class it is generally associated, lacks so many characteristics of vertebrates generally that some naturalists regard it as the type of a separate division. It is of small size (about 3 inches long), compressed, semitransparent, pointed at both ends, without limbs, but with a low fold of the skin, representing the median fin of fishes. The mouth, surrounded by tentacles, is situated below the anterior end of the body, the vent at a short distance from the opposite end. The water which has been received through the mouth for the respiratory function, as well as the spawn, are expelled by another opening in front of the vent (f)orus abdominalis). The skeleton is extremely rudimentary, and consists almost wholly of a simple notochord; neither skull nor ribs or limbs are developed. The lancelet possesses no brain or organ of hearing, and no kidneys. The heart retains the embryonic condition of vertebrates, is tubular and without chambers; the blood is colourless. Thus the lancelet shows unmistakable analogies to invertebrates, among which, indeed, it was placed by its first describer, Pallas; and as, besides, the earliest stages of its development are almost identical with those of invertebrate animals, it may well be regarded as a form intermediate between the two great divisions of the animal kingdom, viz., the vertebrates and invertebrates....