William Evans Hoyle

“ In the great majority of species only one tape-worm head is produced, and such bladder-worms constituted the genus Cysticercus of the older helminthologists. In certain cases, however, notably in the worm which produces the “staggers” of sheep, numerous heads are formed in the wall of each bladder; such larvae formed the genus Cœnurus, but apart from their polycephalous condition there are no structural peculiarities calling for special notice. ”

“ Like any other foreign body, it causes a proliferation of cells, which in due time form a sheath of connective tissue, with a cellular lining, and smooth like a serous cavity within; this covering, however, is not found when the parasite is situated in the brain or the eye. The embryo now grows in size, generally becoming somewhat elongated, and the hooks drop off. Sometimes they can be found lying detached in the connective-tissue sheath. The central cells enlarge and become clear, and in all the Tæniæ they liquefy, forming a quantity of fluid which fills the centre of the bladder-worm. ”

“ The uterus assumes a very different shape as it becomes distended with eggs, which are far too numerous to be contained in a simple straight tube; small protuberances arise from its walls, growing rapidly and bifurcating here and there, so as to produce the complicated branched appearance seen in fig, 1, F. As the uterus grows, the male, and later the female, genitalia degenerate and disappear, and in the proglottides which are ready to be liberated the only organ visible is the distended uterus. ”

“ The organs most often affected are liver and lungs. The adult tape-worm (T. echinococcus) is found in the intestine of the dog, jackal, and wolf, occurring in considerable numbers between the villi. Its length (fig. 3, A) is at most 5 mm. and it consists of only three or four segments; the head has four suckers and a double circlet of hooks.
Pathological Effects.
The pathological effects of Cestodes fall naturally into two categories— (1) those due to the adult worm, and (2) those due to the larvæ or bladder worms. ”

“ The structure of the egg has been best studied in Tænia serrata (Van Beneden, 14) , where it consists of a delicate shell containing a germ-cell, with a quantity of secondary yolk; the former divides into a “granular” cell, which segments no further, and an “embryonic” globe, which again divides into a number of cells, of which three are larger and constitute the “albuminogenous layer,” whilst the remainder are smaller and form the “embryonic mass,” and secrete a delicate superficial cuticle, the cell-limits being indistinct. ”

“ In the embryonic mass from three to five flattened cells form a chitinogenous layer, and give origin to a superficial homogeneous coat, a shell of radially disposed chitinoid cylinders, and an internal faintly striated lining, whilst the remaining cells become the six-hooked embryo or proscolex, a superficial layer to which the hooks belong, and a central mass of clearer cells. ”

“ When the hooks and suckers are fully formed, the head undergoes a process of evagination, so that what was previously a hollow cavity becomes a solid cylinder, and the hooks, which were below the suckers, come to lie above them. Mature bladder-worms vary in size from Cysticercus fasciolaris, the size of a pea, to Cysticercus tenuicollis, six inches or more in length.
The development into the adult tape-worm takes place only after the Cysticercus has been swallowed by the permanent or definitive host. ”

“ The special symptoms of the Echinococcus vary, like those of other bladder-worms, with its situation and size: when it grows within cavities with more or less firm limits compression of adjoining vessels and glandular passages often results, producing œdema, varicose veins, congestion of various organs, or even dyspnœa, if the parasite occur in the thorax. The liver is its most frequent seat, and next the lung; but there is scarcely any organ of the body in which it has not been found, even the bones being sometimes affected. ”

“ The genus Ligula has the segmentation obscure or indistinguishable. About six species are known. One is found encapsuled in a monkey, one in the common seal, others in reptiles and teleosteans. Archigetes sieboldi (fig. 3, B) occurs in the body-cavity of an Oligochætous worm (Tubifex rivulorum) ; it is about 3 mm. long, and consists of an oval body (scolex) , to which is attached a cylindrical tail (proscolex) , bearing at the posterior extremity three pairs of hooks; both these parts are capable of motion. The scolex has eight longitudinal excretory canals, and a terminal vesicle ”

“ The female organs may be most conveniently studied by tracing them inwards from the cloaca. The vagina (v.) opens immediately posterior to the vas deferens, and like it is lined by a continuation of the external cuticle. After passing about half-way across the segment it bends backwards and terminates in a small cyst, the receptaculum seminis (fig. 1, E, r.s.) ; this receives and stores up the male fertilizing elements, retaining them until the ova are ripe. From its posterior extremity there passes a thin-walled canal, wider than the vagina (f.) ”

“ No sooner has the development of the first of these reached a certain degree of completeness than others are formed in similar fashion. The first part of the invagination takes place, by which the future head comes to lie within the brood-capsule and the pedicle is no longer hollow but solid (e) ; the suckers and hooks are, however, still invaginated, and remain so for a considerable period. Seeing that the interior of the brood-capsule is lined with cuticle, it corresponds to the outside of the parent cyst, and hence is probably the representative of a previous invagination. ”

“ Those of the first group are in general slight, being confined to the abstraction of a certain amount of nutriment, and to a more or less acute feeling of irritation, sometimes amounting even to colic-like pains, in the intestine. There have indeed been many authorities who have maintained that they were beneficial ”

“ The nurses develop from little round six-hooked embryos in a more or less complicated fashion as so-called 'bladder-worms.' The latter inhabit very diverse, but usually parenchymatous, organs of the higher and lower animals, and are thence passively transferred to the intestine of their subsequent host" (Leuckart, 1, [1] p. 270) .
Historical Sketch.—Certain forms of Cestodes have been known from time immemorial. The hydatid cyst is alluded to by early medical writers, and Aristotle speaks of examining the tongue of pigs to ascertain the presence of bladder-worms. ”

“ A very remarkable form is Echinococcus multilocularis, which consists of a number of very small vesicles embedded in a common soft stroma; it is found exclusively in man, and for long was regarded as a form of alveolar cancer. ”

“ The muscular fibres are non-striated, and when they are fully developed no nucleus can be detected in them. They taper towards the extremities, sometimes branching dichotomously, and, as above mentioned, a connexion has been asserted to be visible between them and the subcuticular cells.
The excretory system in the proglottides consists of two or four longitudinal canals which lie along their two narrow margins (fig. 1, D, ex.) ”

“ The subjoined arrangement is mainly that of Leuckart. It labours under the disadvantage that its chief divisions are based upon the bladder-worm or larval stage, which is only known in the case of comparatively few species.
I. Cystici (cystic tape-worms) .—Head rarely unarmed; usually provided with a rostellum and with one or more rows of hooks; proglottides longish oval when mature; uterus with median stem and lateral branches; the larva has a caudal bladder containing fluid. ”

“ The first are the best developed, and run down the inner part of the cortical layer in the form of strong bands; the second set lie immediately below them and pass across the body in the form of two flat muscular plates, which converge towards each other as they approach the margins of the proglottis; the sagittal muscles run primitively straight from one flat surface of the body to the other, but their direction is much modified after the growth of the genital organs, between the various parts of which they lie as isolated bundles; they are the weakest of all the sets. ”

“ The main canals open posteriorly into a pulsatile vesicle, at the end of the last proglottis; when, however, some of these have been cast off the opening may be either by a shortened transverse vesicle, as Leuckart (1) maintains to be the case in the present species, or by separate openings, one for each canal.
The reproductive organs are serially repeated in the proglottides, each of which contains a complete set of male and female organs (fig. 1, D) . The male organs may be discussed first. The testes (t., t.) are very numerous and scattered throughout the greater part of the proglottis ”

“ Amphilina foliacea, described as a Trematode by Rudolphi, is found in the body-cavity of the sturgeon. A number of unicellular glands open into the sucker, and are surrounded by the muscles of that organ; the nervous system consists of two ganglia, with a commissure, and two lateral nerves; the male organs resemble those of Bothriocephalus, the female those of the Trematodes ”

“ The segments, like the head, consist of a solid mass of tissue in which the various organs are imbedded. Like the Trematodes, the Cestodes were long thought to have no body-cavity or cœlom, and hence were called "parenchymatous" worms. ”

“ The action of these various structures is not thoroughly understood, but it is probable that the proboscis is protruded by the action of the last-named muscular sheath, whilst it is retracted, after the relaxation of this, partly by the retractor muscle and partly by the pressure of the surrounding medium. ”

“ That due to the invasion and wandering of a large brood of six-hooked embryos has been most successfully studied in cases in which animals have been fed for experimental purposes with fragments of ripe tape-worms ”

“ The mode of its development is unknown (for further information, see Virchow, 17) . Compound bladders occur in man and the ox, whilst other ruminants, swine, and monkeys usually harbour the simple or exogenous forms. ”

“ Phyllobothrinæ.—Suckers without hooks or spines. Examples: Echeneibothrium, Phyllobothrium, Anthobothrium, a few species of each, all from Elasmobranch fishes.
Subfamily ii. Phyllacanthinæ.—Suckers each with two to four hooks. Examples: Calliobothrium, Onchobothrium, Acanthobothrium, two or three species of each genus known from Selachians.
Family VII. Tæniadæ.—Head furnished with four suckers and often with a single or double circlet of hooks; proglottides well-defined and cast off when mature; no uterine aperture. Example: Tænia (see below) . ”

“ A, A segment of Bothriocephalus latus, showing the generative organs from the ventral surface; ex., excretory vessels; c, cirrus; c.p., cirrus pouch; v.d., vas deferens; v.o. vaginal opening; v., vagina; sh.g., shell-gland; od., oviduct; ov., ovary; y.g., yolk-gland ; y.d., its duct; ut., uterus; u.o., uterine opening; the testes are not visible from this side; × 23 (from Sommer and Landois) . B, C, marginal and lateral views of the anterior part of B. cordatus, showing the cephalic grooves; × 5 (from Leuckart) . D, Ciliated embryo of B. latus; × 60 (from Leuckart) . ”