ENTOZOA. 



129 



of all spontaneous movement. The general 

 muscles of the body are disposed in two layers, 

 of which the fibres of the external are trans- 

 verse, those of the internal longitudinal. 



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 lumbricoides, 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 Strongylus 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 striae 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, arid 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 Jig. 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 Porocephalus, and the probo- 

 scides of the Cestoid and Acanthocephalous 

 worms. Of the latter organ the Echinorhynchus 

 gigas offers a good example. The proboscis in 

 this species (Jig. 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 



* Dictionnaire des Sciences Naturelles, torn. iii. 

 App. p. 40. 

 f Anatomic de 1'Ascaride Lombricoide, p. 17. 



VOL. II. 



Retracted proboscis and its muscles, Echynorhynchus 

 gigas. Cloquet. 



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, cT) 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 t&nioides 

 and the larger species of the Nematoidea, 

 especially the Strongylus gigas. 



In the Linguatula 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, /c) 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 



