* Cloquet, Anatomie des Vers intestinaux. Paris, 1824.

(392). The digestive system of the Echinorhynchus is extremely simple. The mouth is a minute pore, placed at the extremity of the proboscis, which communicates with two slender canals, ff, at first of great tenuity, but near the middle of the body assuming something of a sacculated appearance. Towards the tail these vessels gradually diminish in size, until they are no longer distinguishable; but they have not been seen to give off any branches, or to communicate with each other.

(393). Near the origin of these nutrient tubes are two large caeca, nearly an inch in length, called lemnisci (fig. 74,1 & 2, d d), which are probably connected with the digestive function.

(394). The female Echinorhynchus, as is usually the case in Dioecious Entozoa, is considerably larger than the male, as may be seen in the figure. In the former (fig. 74, l), the ovary, c, is a capacious organ, occupying the centre of the body, and extending along its entire length. When minutely examined, it is found to consist of two compartments, or distinct sacs, one occupying the dorsal, the other the ventral aspect - the two tubes being separated by a septum. The dorsal ovary commences near the tail, at g, by a cul-de-sac, and, enlarging as it runs forwards, terminates near the point, c, by uniting with the ventral portion. The anterior part of the canal, b, is common to both divisions of the ovary; and from this the ventral tube runs backwards to the posterior end of the body, where it terminates in a narrow duct, which opens externally at h. It would seem, therefore, that the last-mentioned opening is the only excretory passage from the ovarium, - the connexion apparent in the figure, between the common sac, b, and the root of the proboscis, being merely of a ligamentous character.

(395). In the female of some of the Acanthocephali, according to Siebold1, there are neither proper ovaries nor a uterus, but in their place are found numerous oval or round flattened bodies of considerable size, which float freely in the anterior of the cavity of the body; they have regularly-defined borders, and are composed of a vesicular, granular substance; in these the eggs seem to be formed, so that they may be regarded as so many loose ovaries. When the eggs have reached a certain size, they fall from the ovaries into the cavity of the body, where they continue to increase in size, and become enclosed in additional envelopes. "When mature, the ova escape through a muscular canal, which terminates immediately at the vulva, the latter being a simple aperture, situated at the posterior extremity of the worm. The muscular canal, through which the eggs escape, is of a campanulate or infundi-buliform shape, opening internally by an aperture whose borders float freely in the cavity; of the body and thus the whole apparatus might be compared to a Fallopian tube.

* These muscles are seen of their natural size in fig. 74, 1, at e e. 1 Siebold and Stannius, Comp. Anat. p. 124.

(396). The generative system of the male Echinorhynchus is represented in fig. 74, 2. The organs which secrete the fecundating fluid are two cylindrical vesicles (f, g), attached at one extremity by minute filaments to the walls of the body; from each of these arises a duct (h), and the two, uniting at i, form a common excretory canal. This canal speedily dilates into a number of sacculated receptacles, in which the secretion of the testes accumulates; and from them a duct leads to the root of the penis (m.) The penis or organ of copulation, when extended, protrudes through the aperture (p) placed at the anal extremity of the body; but when retracted, it is folded up and lodged in a conical sheath (o.) The protrusion and retraction of this part of the male apparatus is effected by a very simple mechanism: two muscles (I I), arising from the inner walls of the body, are inserted into the base of the sheath (m), and serve to draw it inwards; and two others (n n), inserted at the same point, but arising from the posterior extremity of the animal, by their contraction force outwards the copulatory organ - an arrangement precisely corresponding with that by which the movements of the proboscis are provided for.

(397). The Turbellariae, constituting another important group of the Helminthozoa, are mainly characterized by having the exterior of their bodies densely covered with vibratile cilia, by the agency of which they swim freely about. They are not parasitical in their habits, and are met with under various forms, both in the sea and in fresh water. They may be divided into two families, the Planariae and the Nemer-tian Worms.

(398). The Planariae:, although they do not inhabit the interior of other animals, are nearly allied in every part of their organization with the Flukes (Distoma); so that their history cannot be more appropriately given than in this place. The Planarise are common in ponds and other stagnant waters; they are generally found creeping upon the stems of plants, or amongst the healthy confervas which abound in such situations, and wage perpetual war with a variety of animals inhabiting the same localities. The body of one of these minute creatures appears to be entirely gelatinous, without any trace of muscular fibre *; yet its motions are exceedingly active, and it glides along the plane upon which it moves with a rapid and equable pace - of which the observer would scarcely expect so simple a being to be capable, - or, by means of two terminal suckers, progresses in the manner of a leech.

* Duges, Ann. des Sc. Nat. 1828.

(399). Many of the larger marine species are able to swim freely in the sea by the aid of violent flappings of the broad margins of their bodies, whereby they beat the water much in the same way as the broad fins of a skate - movements which it would be difficult to explain, except by admitting the existence of a subcutaneous plane of muscular fibres, such as is described by M. de Quatrefages as being recognizable in some species.