. Natural history. Zoology. TAPE- WORMS. 687. system, consisting of fibres that run lengthwise throughout the body, and of others that pass from wall to wall of the segments. It also possesses a nervous and excretory system, the former repre- sented by a ganglion in the head, whence a pair of nerves run backwards along each side of the segments to the end of the body. The excretory organs consist of a circular canal lodged in the head, from which spring four branches, one cor- responding to each sucker ; two of these traverse the sides of the body, and, becoming united in the last segment, ope
. Natural history. Zoology. TAPE- WORMS. 687. system, consisting of fibres that run lengthwise throughout the body, and of others that pass from wall to wall of the segments. It also possesses a nervous and excretory system, the former repre- sented by a ganglion in the head, whence a pair of nerves run backwards along each side of the segments to the end of the body. The excretory organs consist of a circular canal lodged in the head, from which spring four branches, one cor- responding to each sucker ; two of these traverse the sides of the body, and, becoming united in the last segment, open by a common aperture on its hinder edge. They are also put into com- munication with each other in each segment by means of a transverse canal, which runs along its posterior border. Of mouth and alimentary canal there is no vestige, the animal gaining its nutri- ment by absorbing the fluids in which it floata. A Tape-worm is unable to propagate its kind within the host in which it is lodged. But each segment contains a complete set of organs necessary for the purpose, and when it is ripe and breaks off in the manner mentioned above, it is found to be charged with eggs. Such a segment, called a proghttis, makes its way to the exterior, and, bursting, sets free the eggs, which are thus disseminated. Sooner or later some of them, in connection with food or water, are swallowed by a pig. Each egg is then hatched and gives rise to the young known as the proscolex, a minute organism provided with three pairs of hooks (Fig. 12, e). By means of its armature, the proscolex bores it way through the coats of the pig's alimentary canal and enters its blood-vessels. It is then carried by the blood stream to some such organ as the brain, lung, muscles, etc., where it ultimately becomes lodged. Then growth sets in in earnest, the proscolex loses its hooks, and, enlarging, becomes converted into a bladder. Pork thus infested is technically called meaaly (Fig. 12, /). At one point of the bla
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Keywords: ., bookauthorly, bookcentury1800, bookdecade1890, booksubjectzoology
