Although a distinct and general epidermic covering cannot be demonstrated in the more simple Sterclmintha, the soft bodies of which entirely dissolve after a few days' maceration, and which, in animals examined soon after death, are often found in consequence to have lost their natural form, and to have degenerated into a kind of mucus,* yet in most species traces of the epidermic system are manifested in sonic limited parts of the body : thus it ap pears in the form of hard transparent horny booklets around the oral proboscis in the Cystic genera, as in the Cystirrrcus crIlulosat (fig. 61), and most of the Cestoid worms. In the Flori rrps, Ctiv., these recurved spines are arranged along the margins of four retractile tentacles, which thus serve to fix the worm to the slippery membranes among which it seeks its subsistence. In the Trcmatode worms epider mic spines are seldom developed ; the species which infests the human subject ( Distoma hcputirran ) presents no trace of them. When they exist in this order, they are either confined to the head, or are at the same time spread over a greater or less proportion of the surface of the body. Of the first disposition we have an example in the Gryporhynrhus pusillus, (a tre matode worm infesting the intestines of the Tench,) which manifests an affinity to the Terrix armatee in its proboscis armed with six teen strong recurved spines arranged in a double circular series. In the Distoma trigo norepholurn there are two straight spines on each side of the head. In Distoma armatum the bead is entirely surrounded by similar straight spines. In Diatoms ferox the head bears a circle of recurved spines. In Distoma dentirulatum the head is surrounded by a series of large straight spines, and there is a series of smaller spines around the neck. In Dis toma spinulusa the anterior part of the body is beset with reflected spines ; and in the Dis Ionia perlutarn, Nord., the whole surface of the body is armed with booklets, arranged in transverse rows, each being supported on a cutaneous prominence and bent backwards, (see fig. 91).
For a description of the complicated horny and cartilaginous parts of the dermo-skeleton, which enter into the mechanism of the suckers of the worms belonging to the genera Diplu-. zoon and Octobothrium, we are compelled from want of space to refer the reader to IN ordmann's Mikrographische Beitriige, ( Erstcs Heft.) In the Acaathocephala the head, as the name implies, is armed with recurved spines or hooks, which are arranged in quincunx order around a retractile proboscis, (fig. 74) ; and, in addition to these, some species have smaller and less curved spines dispersed over the neck or body.
Among the Calelmintha the genus Lingua tutu is remarkable for the development of four large reflected spines, arranged two on each side the central mouth ; and which can be par tially retracted within depressions of an elon gated semilunar figure. The worm attaches itself so firmly by means of the horny hooks that it will suffer its head to be torn from its body rather than quit its hold when an attempt is made to remove it while alive. In the
Triehorrphalus uncinatus the truncated head presents at its anterior margin a series of hard reflected hooks continued directly from the integument. In the Strongylus ormatus, which has sometimes a singular nidus in the me senteric arteries of the Horse and Ass, the globose head is terminated anteriorly by straight spines, but in the Strongylus dentatus with hooklets. Lastly, we may notice the very singular worm found by Rudolphi in the esophagus of the Water-ben, and which he calls the Strongylus hoz-rictus, where the body presents four longitudinal rows of reflected booklets.
The epidermic processes, when thus traced through the different orders of Entozoa, pre sent but few modifications of form, and have little variety of function ; the straight spines at the mouth serve to irritate and in crease the secretion of the membrane or cyst with which the worm is in contact ; the re curved booklets serve as prehensile instru ments to retain the proboscis and the worm in its position ; and when they are spread over the surface of the body, they may have the additional function of aiding in the loco motion of the species, analogous to the spines which arm the segments of the (Estrus, which passes its larva state, like an Entozoon, in the interior of the stomach and intestines of a higher organized animal.
.2l/riscri/ar syston.—Althougli in every order both of the Parenchymatous and Cavitary worms, living specimens have b:en observed to exhibit sufficiently conspicuous motions, yet the muscular fibre is not always distinctly eli minated in them. In the Cysticari, however, Rudolph' describes two bundles of fibres as arising from the inferior part of the body, and expanding upon the upper part of the cyst. W e have traced corresponding fibres extending to the head in a large Cystirereus tenuieollis; which fibres were doubtless the principal agents in retracting the head within the terminal cyst ; and this part, in the same specimen also, pre sented a remarkably distinct series of transverse stria, indicating most probably the circular fibres which contract the cyst in the transverse direction, and protrude the proboscis.* This species of Hydatid, which is common in the abdomen of Sheep, where it is either sus pended in a cyst to the mesentery or omen turn, or embedded in the liver, &c. has been the subject of numerous observations, and is generally selected to demonstrate the muscular phenomena in an animal of very simple orga nization. When extracted from a recently killed sheep, and placed in water at the blood heat, the cyst may then be observed to become elongated, and agitated with undulatory move ments; the retracted part of the body is thrust forth, and again, perhaps, drawn in ; during the latter action the anterior part of the cyst becomes wrinkled and is drawn back, gliding into the posterior part of the cyst ; the anterior part of the body is at the same time retracted, and is received into the posterior ; and thus by degrees the head and all the body become concealed in the terminal cyst.