These motions in the living worm are vigorous, and easily excited by stimuli; they are therefore abundantly sufficient for the purpose of progression in such situations as those in which the creature lives, and enable it to change its place in the intestines with facility.

(422). Around the mouth or anterior part of the oesophagus there appears to be a delicate nervous ring, probably specially connected with the association of such movements of the oral extremity as are essential to the imbibition of nourishment. From this oral ring proceed two long nervous filaments (fig. 78, e e), one of which runs backwards along the dorsal aspect of the body, while the other occupies a similar position upon the ventral surface. The last-named filament is described by Cloquet as dividing, in the female Ascaris, at the point where the termination of the organs of generation issues from the body (fig. 78, 1, m), so as to enclose the termination of the vagina in a nervous circle.

(423). The digestive apparatus in this order of intestinal worms is very simple. In Ascaris lumbricoides the aperture of the mouth (fig. 78, a) is surrounded by three minute rounded tubercles; into each of these, fasciculi, derived from the longitudinal muscles of the body, are inserted in such a manner as to cause the separation of the tubercles and consequent opening of the mouth, which is again closed by a sphincter muscle provided for the purpose. To the mouth succeeds a short oesophagus (fig. 78, 1 & 2, b), which is separated by a constriction from the rest of the alimentary canal, and would seem, from the muscularity of its walls, to be an agent employed in sucking-in the liquid food upon which the creature lives. The true digestive cavity (fig. 78, 1 & 2, c c) is a simple and extremely delicate tube, which arises from the oesophagus, and, without presenting any appearance indicative of separation into stomach and intestine, gradually enlarges as it proceeds backwards, until it terminates at the hinder extremity of the body by a narrow aperture (fig. 78, 1 & 2, d).

Anatomy of Ascaris lumbricoides.

Fig. 78. Anatomy of Ascaris lumbricoides. 1. Female Ascaris: a, oral orifice; 6, muscular oesophagus; c, alimentary canal; d, termination of ditto at the posterior extremity of the body; e, nervous filaments; k, convolutions of the two ovigerous canals; I, uterine receptacle. 2. Male Ascaris: a, b, c, d, e, as above; f, convolutions of the testes; g, its terminal dilatation, ending in i, the penis.

(424). It would seem that the food of these Entozoa, being already animalized by having undergone a previous digestion, requires little farther preparation; and we are not surprised at finding, in the generality of the Coelelmintha, no accessory glandular apparatus appended to the digestive canal for the purpose of furnishing auxiliary secretions. In two species only have tributary secreting organs been detected. In one example, Gnathostoma aculeatum (Owen), found in the stomach of the tiger, and which is remarkable as possessing a pair of rudimentary jaws, four elongated caeca are appended to the mouth, into which they pour a fluid, analogous, no doubt, to that of the salivary glands*; in a species of Ascaris, found in the stomach of the dugong, Professor Owen likewise discovered a caecal appendage opening into the alimentary tube, at some distance from the mouth, and which, without much stretch of imagination, might be regarded as the first and simplest rudiment of a biliary system 1.

(425). In further prosecuting our inquiries concerning the process of nutrition in these Entozoa, we must now speak of a peculiar structure, first noticed by Cloquet2, and apparently intimately connected with the assimilation of nutriment. Projecting from the inner surface of the abdominal cavity, especially in the dorsal and ventral regions, there are a great number of gelatinous, spongy processes (appendices nourriciers), which, although they have no apparent central cavity, would seem to be appended to vascular canals seen upon the lateral aspects of the body: it is probable, therefore, that their office is to absorb the nutritive juices that exude through the delicate walls of the intestine and convey them into the circulatory apparatus; or they may be reservoirs for nourishment, analogous to the adipose tissue of higher animals.

(426). In the Coelelmintha the sexes are separate; and the generative organs, both of the male and female, exhibit great simplicity of structure. In the female Ascaris, the aperture communicating with the ovigerous apparatus is placed upon the ventral aspect of the body, a little anterior to the middle of the worm (fig. 78,1, m.) This opening leads to a wide canal (I), usually called the uterus; and from the last-mentioned organ arise two long and undulating tubes, which, diminishing in size, run towards the posterior extremity, where they become completely filiform, and, turning back upon themselves, are wound in innumerable tortuous convolutions around the posterior portion of the alimentary canal, until the termination of each becomes nearly imperceptible, from its extreme tenuity. In these tubes, which, when unravelled, are upwards of 4 feet in length, the ova are formed in great numbers, and are found to advance in maturity as they approach the dilated terminal receptacle common to both oviducts (I), from which they are ultimately expelled.

* Owen, Proceedings of the Zoological Society, Nov. 1836.

1 Preparation No. 429 A, Mus. Coll. Surg., Phys. Catalogue, p. 121.

2 Anatomie des Vers intestinaux. Paris, 1824.

(427). The attenuated commencements of the genital tubes in the female Ascaris may be considered as representing the ovary, wherein may be discovered numerous small round cells, which, as they advance forward, begin to be surrounded with a granular vitelline substance, wherein the primitive nucleated cells are still visible: these cells, therefore, ought perhaps to be regarded as germinal vesicles. Still further onward the eggs are of a discoidal shape, and are arranged in a row, or are grouped closely around a rachis that traverses the axis of the ovary. In that portion of the genital canal which may be considered as representing the Fallopian tube the ova become more mature, and subsequently, surrounded by a double colourless envelope, pass into the base of the uterus. This last is the widest portion of the genital tubes, and is distinguished in the living animal by its well-marked peristaltic action. The vagina, distinguishable from the uterus by its narrowness and its muscular walls, opens into the vulva - a narrow transverse fissure, sometimes surrounded by a very remarkable fleshy swelling, generally situated either in front of or near the middle of the body, but in some cases in the vicinity of the anus.