CESTOID WORMS (Lat. ecstas, a band or throng), a family of entozoa, or intestinal worms, of the order Calelmintha (q.v.), consisting of tape-worms and other creatures which resemble them in structure and.habits.. The number of different kinds of C. W.
is great. Their natural history is important in reference to the health of human beings and of the most valuable domesticated animals; and although the subject is not in all respects an agreeable one, it presents much that is interesting and wonderful. Recent discoveries have given it an entirely- new character., C. W., in their most perfect state, when alone they possess the form from which their name is derived, are in reality compound animals, like many zoophytes and asci diens. They do not, however, like these, subsist by food entering the system through mouths with which the individuals composiug it are furnished; for the joints of a cestoid worm, the individuals composing the system or "colony," have no mouth; nor is there any mouth in what is, on various accounts, quite properly regarded as the head, but nutriment is obtained from the surrounding medium by endosmose (q.v.); nourishing juices entering everywhere through the skin, as in the spongioles of the roots of plants, into the cellular tissue or parenchyma of which the whole body consists. The head of a cestoid worm is furnished with organs—different in different kinds—by which it affixes itself to the inner surface' of the intestine of a vertebrate animal. When first it gets into this situation, the body is very short, and has no joints; but they soon begin to appear as transverse strim, and gradually increasing in size, become in most of the kinds very distinct, and at last separate from the system in which they were produced. and are carried away out of the intestines of the animal which contained them. This does not take place, however, till they have not only become mature in the development of the sexual organs—the principal organs to be observed in them—but until they are full of what are called eggs, which, indeed, are rather young ones ready for a separate existence, and each enveloped in a sort of protective shell.. Each joint of a cestoid worm is androgynous. Whilst the most matured joints are thrown off from the posterior end, .new joints are continually formed, as at first, in the part nearest to the head. The number of joints thus formed from a single individual is very great, as will appear when it is considered that tape worms have been found 20 feet long or upwards, and that these have probably been throwing off joints in large numbers before opportunity has been obtained of measuring them.
As the C. W. have no mouth, so they have no alimentary canal. Some of them, as the true tapeworms, have been supposed to imbibe nourishment by the sucking disks of the head; but these are more probably mere organs of attachment, and the canals which are seen to arise behind them, apparently belong, not to the digestive, but to the vascular system, and are united by transverse vessels or vascular rings in the head and in each of the segments. The only trace of a nervous system hitherto observed is a single gan glion in the head, which in some is seen to sendoff nerves to the stickers.
The division into segments remains imperfect in some cestoid worms. Those of the genus ligu/a—chiefly found in birds and fishes—resemble a long flat ribbon, not even notched along the edge, and containing a mere series of hermaphrodite brood-places. When segmentation is perfect, the segments (proglottides), on separating from the parent system (strobila), possess life and a little power of independent motion, creeping away on moist ground, plants, etc. Their period of separate existence, however, is brief; they burst or decay, and the numerous minute embryos which they contain are ready to cotnmence their career, if in any way transferred into the stomach of an animal of proper kind, which is generally different from that whose intestine their parent inhabited. This may happen by their being swallowed—or even the proglottis itself—along with water, grass, etc. Some of the C. W. in this embryo state find their appropriate place in the stomachs of vertebrate, and others in those of invertebrate animals. 1 The shell being broken or digested, the young cestoid worm is set free. It is
extremely unlike the proglottis by which it was generated. It presents the appearance of a vesicle furnished with a few microscopic hooks. It possesses, however, a power of active migration by means of these hooks, and is able to perforate the stomach of the animal which contains it. To this its instinct seems immediately to prompt it, and it is so minute that it passes through the stomach without any serious inconvenience to the animal. It now probably gets into the blood, and is lodged in some of the capillaries, from which it makes its way again by perforation, until it finds a suitable place in some of the tissues or of the serous cavities, in the flesh, or in such organs as the liver or the brain ; and here relinquishing all active migration, it rapidly increases in size, at the same time developing a head, which is in fact that of a cestoid worm, and generally either encysts itself or is encysted—inclosed in a cyst (q.v.)--aecording to circumstances, or according to its species. Great numbers of such parasites are sometimes present in a single animal, causing disease and even death. Until recently, they were regarded by naturalists as constituting species and genera quite distinct from the C. W., of which they are really the young; and the name scolc.r, formerly given to one Of these supposed genera, has now become a common name for the young of all C. W. in this stage, as larva is the common name for the young of insects in their first stage after being hatched from the egg. Those scoliees which inhabit vertebrate animals very generally become distended with a watery fluid, and in this state were formerly regarded as hydatids (q.v.); little else, indeed, appearing without very careful examination, but a small hag filled with fluid, the scolex head being formed within the bag, although capable of being everted from it, as the finger of a glove which has been drawn in at the end is turned out. Such is the young of the common tape-worm (Ionia &ilium), formerly- known to naturalists as cysticercus cellulose', and found in the flesh of the pig and of some other animals, and sometimes of man. It is this scolex, existing in great numbers, which produces in the pig the diseased state commonly known as measly; and it is very unsafe even to handle measly pork in a raw state, because a scolex accidentally getting into the mouth, and thence into the stomach, is likely to become a formidable inmate of the intes tinal canal. It does not appear that this particular species has the power of multi plying in its scolex state, or the circumstances in which it exists in the flesh of the pig may be unfavorable to its so doing, and the prodigious numbers sometimes existing in a single animal have probably all entered by the mouth in the way already described, the contents of a single proglottis or joint of a tape-worm being perhaps sufficient to account for them; but some scolices, as that called ccenurus cerebralis, found in the brain of sheep, and the cause of the disease called staggers—now known to be the scolex of a teenia of the dog—are proliferous by a sort of pullulation, so that clusters of scolices cover the same parental vesicle. Until, however, the scolex reaches the intestine of an animal suited to it, its propagation is entirely unsexual, and no organs of sex exist; but no sooner is it there, than it begins to develop itself into a cestoid worm, and to produce androgynous joints, fertile of new embryos, as already described. Thus we have in these creatures an instance, in its relations the most important known, of the recently discovered alternation of generations. See GENERATIONS, ALTERNATION oF. The transference of the scolex from its place of growth to that in which it becomes a cestoid worm, usually if not always takes place by the animal which contains it being eaten by that whose intestine is suitable to its perfect development. Each kind of cestoid worm is limited to certain kinds of vertebrate animals, and it has been proved by experiment that if introduced into the stomach of other kinds, the scolices soon die. The only C. IV. which infest the human species are bothriocephalus (q.v.) tutus, and tape-worms (q.v.). See Von Siebold's interesting work on tape and cystic worms, printed for the Sydenham society (London, 1857).