The royal natural history . a nemertine, Pterosoma planum (enlarged). trunk it becomes marked by shallow grooves, growing deeper and deeper as theyrecede from the head, until ultimately they divide up the body into a chain offlattened, square or oblong segments, of which there may be many segment is called a proglottis, the whole series being termed muscular system is fairly well developed, and consists of fibres runninglengthwise throughout the segments and across from side to side, and of otherspassing from the upper to the lower walls. By means of these muscle
The royal natural history . a nemertine, Pterosoma planum (enlarged). trunk it becomes marked by shallow grooves, growing deeper and deeper as theyrecede from the head, until ultimately they divide up the body into a chain offlattened, square or oblong segments, of which there may be many segment is called a proglottis, the whole series being termed muscular system is fairly well developed, and consists of fibres runninglengthwise throughout the segments and across from side to side, and of otherspassing from the upper to the lower walls. By means of these muscles the wormis able to shift at will its point of attachment to the gut, and to lengthen or FLAT-WORMS. 461. PILIDIUM LARVA, WITH NEMERTINE WORMDEVELOPING INSIDE. shorten its body to a very considerable extent. The chief centre of the nervous system lies in the head, and from this portion, which may be called the brain, nerves pass forwards to supply the suckers, while a single stout cord runs back-wards on each side to the end of the body, lying close to the edge of the segments. As already pointed out, there is no trace of a mouth nor intestinal canal, although there is an excretory organ, consisting of a ring-shaped vessel in the head, from which four tubes, corresponding in position with the sucker, are prolonged backwards. Two of these soon vanish, but the others lying near the edges of the segments, close to the inner side of the nerve-chords and the longitudinal muscular band, extend to the hinder end of the body, where they unite and communicate with the exterior by a common aperture. At the hinder end of each of the segments these two ducts are united by a third, which runs across f
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
