Ccstoidea.—In the Cestoidca the digestive apparatus commences for the most part by two or four oral apertures, to which, in many spe cies (the Tamar armata), a central uncinated proboscis is superadded, as in the Cysticerci. Sometimes the mouths are in the form of oblong pits or fossw, as in the Bothriocepho Ins lat us, and the allied species grouped tinder the same gene ric name; or they have the structure of circular suctorious discs, as in the Main soliam and other tnie Teniet.t In both genera two alimen tary canals are continued backwards in a straight line near the lateral margins of the body (e, e, jig. 90), and arc united by transverse canals fig.90) passing across the posterior margins of the segments. These connecting canals are relatively wider in the 'fania solium than in the Bothriocephalus lotus, their size apparently depending on the length of the segments, which is much greater in the former than the latter. Neither the transverse nor the longi tudinal vessels undergo any partial dilatations. The chief point at issue respecting the digestive organs of the Tape-worms is, whether the nu triment is imbibed by them through the pores which occur at the sides or margins of each joint, or whether the entire body is dependent for its nutriment upon the anteriur mouths from which the lateral canals commence. The re sults of numerous examinations, which I have made with this view, both on Bothriocephali• and TreniT, have uniformly corresponded with those of Rudulphi, and I entirely subscribe to the opinion of that experienced lielminthologist, that the marginal or lateral orifices of the seg ments are exclusively the outlets of the gene rative organs.
In some species of Tape-worm, as the Tan ia sphernocephalus, in which no ovaria have been detecte%, there has been a corresponding ab sence both of lateral and marginal pores, while the lateral longitudinal canals have been pre sent and of the ordinary size. In the 2'enia solium the generative pores being placed at one or other of the lateral margins of the seg ments, the ducts of the ovary and testis (g, h, Jig. 90) cross the longitudinal canal of that -side, and give rise to a deceptive appearance, as if a short tube were continued from the alimentary canal to the pore. But in the Bothriocephalus lotus and Ilothriocephalus Pythonis the generative pores open upon the middle of one of the surfaces of each segment, and in these it is plain that the lateral nu trient vessels have no communication with the central pores. The orifices of the segments, in short, correspond with the modifications of the generative apparatus, while the nutrient canals undergo no corresponding chaoge. Nutrition may be assisted by superficial ab sorption; and, as Rudolphi suggests,f the se parated segments may for a short time imbibe nutriment by the open orifices of the broken canals ; but setting aside cutaneous absorption and the more problematical action of the rup tured vessels, the head of the Tape-worm is the sole natural instalment by which it im bibes its nutriment, and it is to the expulsion of this part that the attention of the physician should be principally directed, in his attempts to relieve a patient from these exhausting para sites.
Tronatoda.—Four kinds of vessels or canals are met with in the parenchymatous body of the Trematode worms, viz. digestive, nutritive or sanguiferous, seminal, and ovigerous. In the genus Monostonia, the digestive canal is bifur cated, each branch traverses in a serpentine direction the sides of the body, and they are united, in some species, by a transverse com municating vessel at the caudal extremity; in others, as Illonost. mutabile, they converge and terminate in an arched vessel at the posterior part of the body. They are of small size, and not very clearly distinguishable from the sangui ferous vessels.
In the Distoma hepaticum, the digestive organs are more distinctly developed. The (esophagus is continued from the anterior pore, and forms a short wide tube, shaped like an inverted funnel. Two intestinal canals are continued from its apex, which immediately begin to send off from their outer sides short and wide cocal processes, and continue thus ramifying to the opposite end of the body, but have no anal outlet. Rudolphi* states that when successfully injected with mercury, more minute vessels are continued from the apices of the digestive canals, which form a net work over the superficies of the body. A similar dendritic form of the digestive canal obtains in the singular genus Diplozoon, discovered by Nordmann in the gills of the Bream; the central canal and ramified ececal processes in this En tozoon are represented (fig. 328, vol. i. p. 654,) on that moiety, which is opposite the left hand of the observer : on the other moiety the vascu lar system alone is delineated. The latter is not, like the digestive canal, common to both halves of the body, but consists of two closed systems of vessels, each peculiar to its own moiety. Two principal trunks, a, a, traverse the sides of each moiety, preserving a uniform diameter throughout their entire course. In the external vessels marked a, a, Nordmann states that the blood is conveyed forwards or towards the head : in the internal ones, it passes back wards in the opposite direction. The latter vessels commence by many minute branches which unite in the space between the oral suckers and the anterior extremity of the body, and terminate between the disc and suckers at the posterior extremity of the body. The exterior or ascending vessels begin where these disappear and pass towards the opposite end of the body : both trunks freely inter communicate by means of superficial capil laries. The blood moves through them with great rapidity, but without being influenced by any contraction or dilatation of the vessels themselves. The circulation continues for three or four hours to go nn uninterruptedly in each moiety of the Diplozoon, after they have been separated from one another by a division of the connecting band. The blood itself is per fectly limpid. It should be observed, with refe rence to the above description, that the appear ance of circulatory movements in the vessels of the Diplowon paradosum is ascribed by Ehren berg ( Weigmann's Archives, 1835, th. ii.) and Siebold (ibid. 1836, th. ii.) to the motion of cilia on the inner surface of the vascular canals.