In the Cestoidea the muscular structure is indicated slightly by impressions on the sur face of the body, but it is seldom that a distinct layer of muscular fibres can be demonstrated.
To the worms of the genus Caryophylleus both Zeder and Rudolphi agree in ascribing longitudinal fibres, which extend along the anterior part of the body and transverse fibres, which are conspicuous in the pos terior segments. In the Tapia. both trans verse and longitudinal strata of fibrils are stated to exist,t obscure indeed, or almost impercep tible in the smaller species; but more evident in the larger specimens, in which, according to Rudolphi, each segment has in general its own strata, whence it enjoys, for some time after being separated from the rest of the body, distinct and peculiar motions; and such joints have been described as distinct species of En tozoa, under the name of Cueur bitinie. In the Bothrioeephalus lotus, on the other hand, the lon gitudinal fibres are continued from one joint to another, whence the segments are less readily separable, and a common and continuous co vering may be dissected from off the body of this species.
Living Twniw placed in warm water exhibit undulatory motions. The body of one of these worms is sometimes found to be tied at some part in a complicated knot, as seen in fig. 75, doubtless by means of these motions. The Tapia when recently expelled from the body by the irritation of a vermifuge remedy, is occasionally contracted to the length of a few inches, the segments appearing as close-set transverse strive ; when placed in water, after a few hours it will have returned to a length of as many feet. Werner• relates an instance of a Twnia which extended from the anus of a patient to the length of three feet, and which returned itself almost wholly into the intestine, the dependent part being drawn upwards by the superior. Other and still more extraordinary instances of the movements of the Cestoid worms are on re cord ; but that the separated joints of the Tsenia soliwn should be able to creep several feet up a perpendicular wall could scarcely gain a mo ment's credit, if the fact were not related by no less distinguished a naturalist than l'allas.t
In general the muscular fibres cannot be observed in the diaphanous bodies of the smaller Tremaloda, yet every part is endowed with active contractility: in the larger species, however, both longitudinal and transverse strata of fibres, may be demonstrated in the tegumen tary muscular covering of the body ; both which we have distinctly seen in the large Distorna clavatum. The muscular fibres of the aceta hula are disposed in two series, one radiating from the centre to the circumference, the other in concentric circles. The muscular tissue is also well developed around the base of the sucker, by which the animal is enabled to pro trude them from the surface.
In the Planarix, in which, as in the Teenitr, according to our observations, the muscular system is indicated only by striae on the super ficies of the apparently homogeneous paren chyma, the phenomena of muscularity are strikingly displayed in the varied and energetic actions of the living animal. They lengthen, shorten, widen, contract, or contort the body in various degrees and directions : their mode of locomotion on a solid plane is by an insen sible undulation, or successive approximation of small proportions of the body, producing a gliding movement, as in the Slug; and the same actions take place in swimming through the water, except that the body is reversed ; and the ventral surfhee turned upwards, as in the Carinaria and other aquatic Gastropods. When seizing a living prey, as in fig. 76, the contractions of the body are more vigorous and extensive.
In the Echinorhynehus the muscular fibres are of a whitish colour, transparent, and of a latinous appearance; they are eminently contractile, and readily respond to the application of both chemical and physical stimuli. Cloquet served them to contract under the influence of the galvanic current six hours after the cessation 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.