The excretory vessels of the scolex are continuous with those of the proscolex. The latter appear to form a network, and open posteriorly by a pulsatile vesicle. The contents of the excretory canals, when extruded from the pulsatile vesicle or the foramina secundaria, appear to be immiscible with water. The granules suspended in the liquid are sometimes calcareous in nature (see p. 227).

1The ganglia of Solenophorus appear to be differently arranged to what they are in other Cestoda. See Griesbach, A. M. A. xxii. 1883. The 'plasmatic canals' of Sommer, found by him in T. solium and T. mediocanellata, are perhaps to be identified with the lateral nerves. See note, p. 515, Z. W. Z. xxiv. 1874. The nerves from the ganglia of T.plicata are said by Rhemberg to end in the cuticula as delicate threads, terminated each by a slight swelling (Arch. f. Thierheilkunde, iii. 1877, P- 43)- Sensory nerve endings and motor nerve endings have been described by Schiefferdecker (J. Z. viii. 1874, pp. 475-480). But the results of these two observers have not been as yet confirmed by others.

1According to Moniez ('Les Cestodes,' p. 185 et seqq.) the ventral vessel in Taeniae belonging to the type of T. serrata becomes lacunar; the dorsal appears to vary much. The cross anastomosis mentioned later on connects only the ventral vessels. But in the abortive joints of T. crassicollis and in Tetrarhynchus claviger both vessels have their cross anastomoses, which may fuse medianly; and in the first-named there is evidence for a connection between the ventral and dorsal vessels, establishing thus a circular communication.

All Cestoda are hermaphrodite. The male organs consist of a large number of vesicular testes, of delicate efferent canals, of a vas deferens which receives the latter and terminates in an evaginable portion or 'cirrus' surrounded by a muscular envelope or 'cirrus sac.' The testes are more or less globular, numerous, i. e. several hundreds in each joint of a large tapeworm, but in the tapeworms of Birds especially only 2-3, scattered, and usually confined to one aspect of the body - hence termed dorsal (supra). The vasa efferentia are extremely fine tubules, difficult to see unless naturally injected with sperm. They unite inter se, but eventually open by a larger or smaller number of canals into the vas deferens. This organ may be single, or, as in Schistocephalus and Ligula, double. It becomes as sperm collects, disposed in loops or coils, and at the same time dilated, especially towards its termination. In Bothriocephalus latus, Schistocephalus, and Ligula the dilatation or vesicula seminalis is surrounded by an envelope of chiefly longitudinal muscle-fibres and forms a globular or ovoid body. The termination itself of the duct is single, usually slightly coiled and is evaginable; the evaginated portion constitutes the cirrus or penis.

The outer surface of the cirrus (the inner before evagina-tion) is in some instances armed with spines, e. g. in Echeneibothrium. The female organs consist of two ovaries or germaria, of vitellaria, or the homologous 'albumen gland,' a shell gland, uterus, vagina, and sperma-theca. The germarium is rarely single, as in Caryophyllaeus and Ligula. It consists either of branching anastomosing tubes, as in the larger Taeniae, Bothriocephalus, Schistocephalus, and Ligula, or of a small number of vesicles attached to a slender duct, as in Taeniae, with narrow joints, e. g. T. perfoliata; or it may be vesicular, and either lobed, e. g. T. lineata, or simple as in Caryophyllaeus. The vitellarium has much the same structure as the germaria in most Taeniae, e. g. T. solium, T. mediocanellata, and is a single gland placed near the posterior margin of the joints 2. In other Taeniae it is vesicular, e. g. T. echinococcus, and may be double, e. g. T. lineata. It may have the form of a series of vesicles ranged along either side of each joint, each series with its own duct ( = vitello-duct), the two ducts uniting, as is the case in many tape-worms inhabiting fish, e. g.

Tetrarhynchidae, Tetraphyllidae, Caryophyllaeus. Or, as in Bothriocephalus and Ligula, etc. it consists of a large number of vesicles, lying close under the subcuticula, and scattered over the sides of both aspects of the joints in Bothriocephalic, over the dorsal aspect and the sides of the ventral aspect in Schistocephalus and Ligula. The vesicles are connected by a network of ductules from which a number of ducts proceed and unite into a common vitello-duct1. The shell gland or 'Mehlis' gland' usually consists of a large number of unicellular glands surrounding at one point and opening into, the duct leading to the uterus. In T. lineata however it consists of an inner layer of radial columnar cells and an outer of cells more or less flattened. The uterus, apparently absent in Caryophyllaeus, is a tube disposed in Taeniae with narrow joints, e. g. T. perfoliata, cross-wise, but in other instances lengthwise, in the joints. It is convoluted and opens externally by a separate aperture of its own in the Pseudophyllidea, but in all other Cestoda it is closed, and as the ova accumulate, it increases in size and may develope lateral offsets, especially in the larger Taeniae, or it may become divided into several portions 2. The vagina is a narrow tube, of variable length, sometimes convoluted, often provided with internal hooks or spines, and in most instances dilated at its inner end to form a receptaculum seminis or spermatheca.

In Schistocephalus and Ligula, however, there appears to be no special dilatation, but sperm collects at various points in the course of the tube. The innermost extremity of the vagina generally ends in a tube which receives (I) the ducts of the germaria, (2) the vitello-duct, and (3) the shell-gland, close to the commencement of the uterus. Certain Taeniae, sometimes termed generically Dipylidium, e. g. T. elliptica of the dog, have in every joint a right and left set of genital organs. But the uterus is common to the two sets and has the form of a network with marginal caeca, and the germarial ducts also enter the receptaculum seminis. The external apertures of the cirrus and vagina are placed close together, usually in a depression surrounded by a more or less prominent margin. The depression or sinus genitalis has a single external pore. It is placed commonly on one of the margins of the joints, frequently alternating from one side to the other in successive joints. Or it is placed on the ventral aspect of the joints as in some Taeniae3, and in the Pseudophyllidea except Triaenophorus. The aperture of the cirrus into the sinus genitalis usually lies in front of, or anteriorly to, that of the vagina, but in some of the Taeniae with narrow joints the two apertures are side by side, e.g. in T.perfoliata1. In Schistocephalus and Ligula the male and female apertures are ventral, but there is no sinus; the uterus opens near to them and all three apertures are in the adult disposed in a straight line crosswise, but not always in the same order from right to left.