With respect to the disposition of the mus cular system of the Nematoid worms, a dif ference of opinion is entertained by some ex perienced comparative anatomists.
Professor De Blainville* describes, in the Ascaris lumbricoidcs, the external stratum of muscular fibres as being longitudinal, while the internal, he observes, are evidently trans verse, and much more numerous at the an terior than the posterior part of the body. M. Cloquet, on the contrary, in his elaborate monograph on the Ascaris lumbricoides, states that the exterior layers of muscular fibres are transverse, and the internal longitudinal. In a large specimen of the &rangy/us gigas, Rud., which we have dissected and examined micro scopically for the muscular system, we find that a very thin layer of transverse fibres ad heres strongly to the integument, the fibres being imbedded in delicate furrows on the internal surface of the skin ; within this layer, and adhering to it, but less firmly than the transverse fibres do to the integument, there is a thicker layer of longitudinal fasciculi, which are a little separated from one another, and distributed, not in eight distinct series, but pretty equally over the whole internal circumference of the body. Each fasciculus is seen under a high magnifying power to be composed of many very fine fibres, but these do not present the transverse stria which are visible by the same power in the voluntary muscular fibres of the higher animals. The longitudinal fibres are covered with a soft tissue composed of small obtuse processes, filled with a pulpy substance, and containing innumerable pellucid globules, and at the an terior extremity of the body this tissue assumes a disposition as of transverse fasciculi ( fig. 79). In the Ascaris lumbricoides similar internal transverse bands are shown in fig. 88, e, e, and are those which Professor Blainville regards as muscular, and Cloquet as vascular organs. We cannot detect a tubular structure in these parts, neither have they the texture and con sistence of the true fibrous parts : they are soft pulpy substances, doubtless connected with the nutritious functions, and probably the or gans of absorption.
Besides the general muscular investment of the body, there are distinct muscles in most of the Entozoa, developed for the movement of particular parts, as the retractile hooks of the Linguatula and Porocepimlus, and the probo scides of the Cestoid and Acanthocephalous worms. Of the latter organ the F,chinorhynchus
gigas offers a good example. Theproboscis in this species (fig. 77) is a short, firm, elastic, cylindrical tube, buried with its appropriate mus cles in the neck of the animal, as in a sheath; and having its anterior extremity (a, b) terminated by a spherical eminence armed with four rows of recurved spines. The retractor muscles are four in number, two superior and two inferior, (f, g,) flattened, elongated, and of a triangular figure. They are continuous at their base or posterior extremity, with the longitudinal fibres of the body ; their anterior extremity, which is extremely delicate, is inserted into the poste rior part of the proboscis. The protractile mus cles (c, d) are also four in number, short but strong, and forming, as it were, a sheath to the proboscis ; they are attached to the anterior part of the tegumentary sheath, and pass back wards to be inserted into the posterior extremity of the proboscis in the intervals left by the retractor muscles. The motions of the pro boscis thus liberally supplied, are, as might be expected, more lively than those exhibited by any other part of the body. When it is drawn back into its sheath by means of the retractor muscles, the booklets seem to be drawn close to the side of the bulbous extremity, whence we may infer that these also have their appro priate muscles.
Nervous system. —The Entozoa in which the nerves can be most easily and distinctly demonstrated, are the Linguatula tenioides and the larger species of the Nematoidea, especially the Strongylus gigas.
In the Lin$uatula a proportionally large ganglion (g, fig. 78) is situated immediately behind the mouth, and below the oesophagus, which is turned forward in the figure, at o; small nerves (h, i, k) radiate from this centre to supply the muscular apparatus of the mouth and contiguous prehensile booklets; and two large chords (/, /) pass backwards and extend along the sides of the abdominal aspect of the body to near the posterior extremity, where they gradually become expanded and blended with the muscular tissue.