TAPEWORM is a word popularly used in a vague sense to designate any worm of the group eestoidea (see CESTOID Worms). According to Dr. Cobbold, upward of 250 distinct forms of cestoid worms have been described, of which probably somewhat less than 200 may be regarded as really good, species. These he divides into the three families of (1) taniadte, or true tapeworms; (2) bothriocephalida, and (3) tetrarhynohkles. For the natural history of the tapeworms generally, we must refer to the article CEsToro WORMS. We will here only remind the reader of the following points necessary for the due understanding of this article, and that every tapeworm passes through several distinct phases during its life-history. "In the ordinary colonial or tapeworm condition," says Dr. Cobbold, "it has been termed the 'strobila (Van Beneden). The separate joints of which the strobila is composed are denominated proglottides, or zooids. The anterior segment forms the head, and remains barren, those of the neck and front part of the body being sexually imma ture during the process of strobile-formation. The mature proglottides at the caudal end are capable of realizing an independent existence, and the eggs which they contain develop the six-hooked embryos, or proscolices (Van Beneden), in their interior. These latter become metamorphosed into scolices or nurses, representing• the well-known cysti cereal state, which, in its sterile or aborted condition, forms the common hydatid."— Entozoa, p. 105. During the greater part of their existence, the tapeworms are parasitic animals, the mature proglottides and eggs being free only during a comparatively short interval. They are mostly restricted in their distribution to the vertebrate animals, com paratively few of the invertebrates (excepting the cuttle-fish) appearing to harbor them in their adult condition, although the tapeworm larva;, nurses, or scolices probably abound in various invertebrate groups. In the human body, no less than ten species of tapeworm occur, viz., eight true tapeworms, and two species of bothriocephalus; and as four distinct species have been found in the Barbary ape, it is obvious that errors of diet, due to civilization, are not the cause of these parasites. Among the animals with which we are
most familiar, the 'species are plentiful in the common dog (and in true carnivora gener ally). in rats, and mice. The typical ruminants are almost constantly invested both by mature and immature forms; while the larger pachyderms, and solidungulates (the horse, ass, etc.). harbor only a few adult forms; but only larvae appear to be known in swine. These worms appear to be as abundant in granivorous birds as in carnivorous hawks, owls, etc. In the water-birds generally, the adult worms are very abundant, their larvae existing in the food of such birds, in fishes, mollusks, etc. In reptiles, these worms are extremely rare, although other parasitic worms abound; while in fishes they are very abundant both in the adult and larval forms.
The taniacke, or true tapeworms, may be distinguished from the other families of the order cestoidea (cestoids or tapeworms in the popular sense) " by the possession of a small distinct head, furnished with four simple oval or round suctorial disks (suckers), and commonly also with a more or less strongly pronounced rostellum (proboscis) placed at the summit in the median line. This prominence, when largely developed, becomes retractile, and in use, is lodged within a fiask-shaped cavity, lined by a sheath, and supplied with special muscles; it is also very frequently armed with a single or double crown of horny chitinous hooks, there being occasionally as many as five or six separate circular rows of these organs. Attention to the number, relative size, and dis position of the hooks is often sufficient to determine the particular species. In nearly all cases the reproductive orifices are situated at or near the margins of the joints which are bisexual."—Cobbold, op. cit., p. 109. The eight true tapeworms occurring in man are (1) Tania solium, Linnmus; (2) T. mediocanellata, Ktichenmeister; (3) T. acanthotrias, Weinland; (4) T. flavopuncta, Weinland; (5) T. nana,Von Siebold ; (6) T. elliptica, Batsch; (7) T. marginata. Batsch; (8) T. echinococcus, Von Siebold.