* The moniliform character which these vessels exhibit is produced by the process of dissection. If, in the ordinary way, a longitudinal dorsal incision is made, and the two halves be then separated and pinned down, the vessels under such tension are sure to assume a moniliform outline, that is, one part will dilate and the other contract, and so on successively throughout the whole length of the vessels: the dilated portion will be filled with blood, and the contracted will be empty, and the beaded figure will be perfect. If, however, a more careful mode of opening the worm be adopted, dividing, by means of fine scissors, the membranous segmental partitions, and laying gently open the integuments, these vessels will present a perfectly smooth outline: if, now, one of them be seized with the forceps and slightly pulled, it will become irregularly knotted, or moniliform. Muscular fibres, chiefly circular, are present in their parietes, and it is to the uneven action of these elements that the beaded form is attributable. - Dr. Williams.

(605). On reviewing the above arrangement, we immediately perceive that, notwithstanding the similarity observable in the distribution of the ventral and sub-ganglionic systems of vessels, in a physiological point of view they are subservient to very different functions - the former representing the systemic, the latter the pulmonary circulation. The blood derived from the dorsal trunk by the moniliform hearts (d) is supplied by the ventral vessel (which may be compared to an aorta), over the surface of the viscera; and the remnant of this blood, after furnishing materials for nutrition, is returned to the dorsal canal by the deep vessels (e, g); but that portion of the circulating fluid which passes from the termination of the dorsal tube into the sub-ganglionic trunk not only serves for the nourishment of the skin and muscular integument, but at the same time is brought in contact with the air as it passes through the cutaneous network, and is thus more or less replenished with oxygen before it is again returned to the general circulation.

The sub-ganglionic canal is therefore a kind of pulmonary artery, and the dorsal drives to the moniliform vessels a mixed fluid, composed partly of venous blood derived from the viscera, and partly of arterial derived from the superficial or sub-cutaneous system.

(606). Consequently in the Lumbrici the primary longitudinal trunks are similar in number and disposition to those of the Leech, and the direction of the blood-current is almost the same. The intestine in the Earthworm (in this respect distinguished from the Leech) is only tied to the integuments at the interannular points, the intervals or segmental spaces being left as chambers (fig. 1ll, v v) containing a small quantity of viscid corpusculated fluid, which is the peritoneal fluid of this worm. The interposition of a fluid stratum in this part involves other anatomical modifications, which still further separate the organization of the Earthworm from that of the Leech; the spongy vessels described above as occupying this part in the latter are absent in the former.

(607). Superadded to the primary median blood-channels (fig. 113, a, b, c, d), a minor lateral system, founded upon the latero-abdominal trunk, may be demonstrated in the Earthworm as in the Leech: in all essential particulars, in the two cases, the main trunk of the system and its branches are the same.

(608). Few points connected with the history of the Earthworms have given rise to so much speculation as the manner of their reproduction. The generative organs have long been known to be lodged in the anterior part of the body, their position being indicated externally by a considerable enlargement or swelling that extends from the seventh to about the fourteenth segment, counting from that in which the mouth is situated. On opening this portion of the animal, a variable number of white masses are found, attached to the sides of the crop and gizzard (fig. Ill, hhJi); these have long, by general consent, been looked upon as forming the reproductive system - some having been regarded as representing the testes, others the ovaria: yet so delicate are the connexions which unite these glandular masses, and such the difficulty of tracing the ducts whereby they communicate with the exterior of the body, that the functions to which they arc individually appropriated have given rise to much discussion. The Lumbrici have been generally acknowledged to be hermaphrodite, that is, possessed of organs adapted both to the formation and fertilization of ova; and it is likewise well understood that the congress of two individuals is essential to the fecundity of both, as, in the earlier summer months, the mode in which they copulate is a matter of constant observation.

At such times two of these animals are found to come partially out of the ground from contiguous holes, and, applying together those segments of their bodies in which the generative glands are situated, are observed to remain for a considerable time in contact, joined to each other by a quantity of frothy spume which is poured out in the neighbourhood of the sexual swellings. No organs of intromission, however, have ever been distinguished; neither, until recently, had the canals communicating between the sexual orifices and the testicular or ovarian masses been satisfactorily traced; so that Sir Everard Home* was induced to believe that, in the kind of intercourse above alluded to, there was no transmission of impregnating fluid from one animal to the other, but that the excitement produced by mutual contact caused both the ovaria and testes to burst, so that the ova escaping into the cells of the body became there mingled with the spermatic secretion, and being thus fertilized, were hatched internally, and the young, having been retained for some time in the cells between the intestine and the skin, were ultimately ejected through apertures supposed to exist in the vicinity of the tail.