. Outlines of zoology. Zoology. 412 CEPHALOCHORDA. and other small organisms, which are sucked into the mouth. At times, especially in the evening, the adults start up and swim about, but they are never so active as the larvae. The early embryo is pelagic. It is of interest to note that along with lancelets, specimens of the Annelid Ophelia are often obtained; they closely resemble lancelets, not only in shape and size, but also in the way they burrow and swim. Form.—The body, between \\ and 2 in. in length, is pointed at both ends, as the names suggest. The living animal is translucent, with
. Outlines of zoology. Zoology. 412 CEPHALOCHORDA. and other small organisms, which are sucked into the mouth. At times, especially in the evening, the adults start up and swim about, but they are never so active as the larvae. The early embryo is pelagic. It is of interest to note that along with lancelets, specimens of the Annelid Ophelia are often obtained; they closely resemble lancelets, not only in shape and size, but also in the way they burrow and swim. Form.—The body, between \\ and 2 in. in length, is pointed at both ends, as the names suggest. The living animal is translucent, with a faint flesh colour, and is much plumper than a spirit specimen. The muscles are arranged in sixty-two segments or myotomes. There are three un- paired apertures—(a) the median, ventral, pre-oral hood over-arching the true mouth, and fringed with tentacle-like. G. Fig. 177.—Lateral view of Amihioxus.—After Ray Lankester. The notochord runs from tip to tip. t., Tentacular cirri; G., reproductive organs; , atriopore; a., position of anus ; 40 and 62, indicate number of myotomes. cirri; (6) the atriopore in myotome thirty-six, giving exit to the water which enters by the mouth; (c) the anus, ventral and slightly to the left, behind the atriopore, but some distance from the posterior end of the body. Along the back there is a median fin, which is continued around the tail, and along the ventral surface as far as the atriopore. In front of this region the ventral surface is flattened, and fringed on either side by a slight fin-like " metapleural" fold. These folds are continuations downwards of the walls of the atrial or branchial chamber, which extends from behind the mouth to the atriopore, and into which the gill- slits of the pharynx open in the adult. Skin.—The epidermis consists of a single layer of cylin- drical cells. Some of them project slightly from the surface, and are connected at the base with nerve fibres. These are sensory cells, and may be c
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
