In Taenia lineata the cuticula has the same structure as in Solenophorus. There is a similar matrix which is finely granular. It contains large granular, oval, round or amoeboid cells, small fusiform or stellate cells, and scattered nuclei with or without traces of surrounding protoplasm. Tubular or vasiform spaces filled by a granular material lie immediately beneath the cuticula: they sometimes occur empty. There is also a layer of vertically spindle-shaped sub-cuticular cells which give origin to (?) the cuticula. They lose their individuality if the specimen is preserved only in alcohol. The deep longitudinal muscle-fibres are grouped in bundles and retain no trace of their formative cells, as do the dorso-ventral and circular muscle-fibres (Hamann). T. serrata has not been investigated by modern methods with reference to these points. The term 'parenchyma' is often used in speaking of the connective tissue substance of Cestoda. It is better discarded as the tissue in question is not cellular in structure.
The nervous system of T. serrata has been carefully investigated by Niemiec. It consists, as in some other Taeniae, of the following parts. A nerve-ring lies a little below the base of the rostellum. It gives off nerves to the muscles of the hooks, and contains eight slight ganglionic enlargements from each of which originates a stoutish nerve passing backwards. Two pairs of these nerves (A, A: A, A), situated at opposite extremities of the same diameter of the ring, unite each with one of the two lateral principal ganglia. The other two pairs (B, B: B, B) unite with the secondary transverse commissure and the polygonal commissures (infra). The two lateral principal ganglia are connected by a primary transverse commissure in the middle of which is a voluminous central ganglion. This ganglion gives origin to a slender secondary transverse commissure which lies at right angles to the primary transverse commissure and forks at either end. Each branch of the two forks unites with one of the nerves B, B, etc. supra, and with the superior polygonal commissure. The lateral principal ganglia and the nerves B, B, etc, are united by two ring-like polygonal commissures, one superior, the other inferior.
The points of union of the nerves B, B, etc, with the secondary transverse and the polygonal commissures are swollen and form secondary ganglia, from which, as well as from the lateral principal ganglia, nerves are given off to the suckers
The nerves B, B, etc, are continued backwards through all the joints as slender filaments, two on each surface. Three longitudinal lateral nerves, a median stout nerve with a slender nerve on either side, extend backwards in a similar manner, and lie to the outer side of the longitudinal excretory trunks. They are said to degenerate in the ripe joints by Hamann. It is possible that branches may originate in some instances from the lateral nerves. Riehm states that they possess a swelling close to the posterior margin of each joint in Dipylidium pectmatum (=T. pectinata in part) of the Rabbit from which nerves pass both inwards and outwards. Similar swellings exist in Ligula and Schistocephalus (Kiess-ling). Their ganglionic nature is by no means certain.
The nervous system of Bothriocephalus and Ligula is said to be simpler than that of the Taeniae.
The excretory system of T. serrata appears to correspond in its main features with that of most Taeniae, a general description of which is given in the account of the Class Cestoda. Ciliated funnels have been detected by Fraipont in this Tapeworm and in its Cysticercus (Archives de Biol. i. 1880, p. 439). Leuckart figures the anterior anastomosis between the longitudinal vessels as consisting of a ring-like vessel with branches in connection with it (Parasiten (ed. 2), i. p. 379, fig. 153). Two longitudinal vessels are certainly present, perhaps four. P. J. Van Beneden does not figure a cross anastomosis at the posterior margin of each joint, nor does he mention the presence of valves; points which lack of material has prevented me from determining. He mentions, however, that treatment of the scolex with acetic acid causes an evolution of Carbon dioxide in the excretory canals which escapes by the foramen caudale or aperture of the pulsatile vesicle.
Peculiar rounded or elliptical bodies of a bright refractile appearance are found in the head and neck, and in the joints, especially the young joints, of all Cestoda. These bodies are very numerous in T. serrata. They are found principally in the superficial part of the connective tissue, but may occur also in the more central part where they are absorbed on the evolution of the sexual organs. They often show concentric lines like those of starch granules, and under the action of an acid they give off a gas, Carbon dioxide, which exists in combination with lime. Hence the name Calcareous bodies given to them. They contain a small amount of organic matrix, and are believed to be either calcified cells or portions of calcified cells. They lie, according to Griesbach, in the lacunae of the connective tissue, and he appears to think that they may enter the excretory system through direct communications between its cross anastomoses and the coelomic lacunae. It is certain that the excretory canals contain calcareous particles, and in certain Trematoda their branches have appended ampullae, in which lie calcareous bodies similar to the calcareous bodies of the coelomic lacunae in the Cestoda. The function of these structures is unknown; it may be partly excretory, partly skeletal.
For the generative organs of a Taenia, see Pl. xiv. (post), figs. 2 and 3.
The structure and development of the ovum in T. serrata have been carefully studied by E. Van Beneden. It consists of a delicate shell containing a germ or ovum-cell together with a quantity of a hyaline, homogeneous and colourless albumen or deutoplasm (=secondary yolk). The germ segments into two cells, one transparent, the 'embryogenic globe,' the other a 'granular cell,' which segments no further. The former of the two divides, and the result of its division is a number of cells of which (1) three are larger and constitute the 'albumino-genous layer;' (2) the remainder are smaller and constitute the 'embryonic mass.' The three cells (1 supra) enlarge and surround together with the 'granular cell,' the 'embryonic mass,' and secrete a delicate superficial cuticle, the cell-limits becoming indistinct. In the 'embryonic mass' there are three, four, or sometimes five flattened cells placed laterally and containing, unlike the remaining cells, nucleolated nuclei. These cells constitute a 'chitinogenous layer.' They give origin to (1) a superficial homogeneous coat; (2) a coat or shell of radially placed juxtapposed chitinoid cylinders which increase in length at the expense of (3) an internal faintly striated coat in which lie the degenerating nuclei of the chitinogenous cells.
The remaining cells of the 'embryonic mass' become the hexacanth embryo or proscolex, as it is called, and are arranged in an incomplete superficial set of more granular cells, and a contained set of clearer cells which protrude at one pole, but are probably grown over subsequently. The three pairs of hooks belong to the superficial set of cells. When the proscolex is mature the original egg-shell and the albuminogenous layer of cells disappear, and it remains invested solely by its chitinoid coat. The ova of some other Taeniae, e. g. T. mediocanellata s. saginata, appear to have a similar development. The ovum sometimes undergoes regular and equal segmentation, e. g. in T. bacil-laris, and then the albuminogenous layer is formed by a layer of numerous cells raised from the surface of the embryonic mass. For figure of proscolex, see Pl. xiv. fig. 4.
Van Beneden regards the albuminogenous layer of cells as the homologue of the ciliated coat of cells or 'embryophore' of some species of Bothriocephalus, of Schistocephalus, and Ligula. Moniez, on the other hand, considers the chitinogenous set of cells as the homologue of the same structure; but he missed the albuminogenous coat in T. serrata, etc, though he appears to have detected it in other Tapeworms. Leuckart's account agrees essentially with Van Beneden's. The latter thinks the successive coats of cells, formed as above, are to be considered as layers of ectoderm cells thrown off one after the other.
The last joints of a Taenia contain the uterus alone of all the genitalia, laden with the proscolices contained within their chitinoid coats. They are detached either singly or in small numbers. For their subsequent fate, see next Preparation. Some Cestoda possess a uterine aperture, and the ova are consequently discharged at an earlier stage, e. g. Bothriocephalus.
Parasites of Man and diseases resulting from them, Leuckart, transl. by W. E. Hoyle, Edinburgh, i. 1886; the German original 'Parasiten des Menschen,' i. (ed. 2), 1881; ii. 1876. Parasites, Cobbold, London, 1879. Vers Intestinaux, P. J. Van Beneden, Paris, 1858 (or Supplement aux Comptes Rendus de l'Acad. des Sci., ii. 1861); Vers Cestoides, Id. Mem. de l'Acad. Roy. Belg. xxv. 1850. Les Cysticerques, Moniez, Travaux Inst. Zool. Lille, iii. 1, 1880; Les Cestodes, Id. pt. 1, ibid. iii. 2, 1881.
Lists of Parasites and Hosts, von Linstow, Compendium der Helminthologie, Hannover, 1878.
Cestodes of Hares and Rabbits, Riehm, Inaug. diss. Halle, 1881 (Zeitschr. f. d. ges. Naturw. Giebel, 54, 1881). Taenia lineata, Hamann, Z. W. Z. xlii. 1885. T. perfoliata, Kahane, Z. W. Z. xxxiv. 1880. Solenophorus, von Roboz (Beitrage, &c), Z. W. Z. xxxvii. 1882; Griesbach (Beitrage), A. M. A. xxii. 1883. Triaeno-phorus, Megnin, Journal de l'Anat. et Physiol., 1881. Ligula and Schistocephalus, Kiessling, A. N. 48, 1882.
Suckers, Niemiec, Recueil Zool. Suisse, ii. 1885. Connective tissue, etc, Griesbach, on Solenophorus (supra). Ditto, and muscular tissue, Hamann on lineata (supra).
Nervous system, Niemiec, Recueil Zool. Suisse, ii. 1885; cf. Lang, Mitth. Zool. Stat. Naples, ii. .1881.
Excretory system, Fraipont, Archives de Biol. i. 1880; ii. 1881. Pintner (Untersuchungen, &c), Arb. Zool. Inst. Wien, iii. 1881.
Coelome, Fraipont, op. cit.; cf. Van Beneden and Ray Lankester, Z. A. iv. 1881; v. 1882. Griesbach on Solenophorus (supra).
Sexual organs of T. mediocanellata (=saginata) and T. solium, Sommer, Z.W. Z. xxiv. 1874; of Bothriocephalus, Id. and Landois, Z. W. Z. xxii. 1872.
Development of proscolex from ovum in T. serrata, E. Van Beneden, Archives de Biol. ii. 1881. For general account, see Moniez, Travaux Zool. Inst. Lille, iii. 2, and Leuckart (supra).