Page:Encyclopædia Britannica, Ninth Edition, v. 21.djvu/15

Rh EOTIFEEA particles, and deposits in a regular oblique or spiral series, and which are cemented together by a special secretion. The urceolus serves as a defence, as the animal can by con- tracting its stalk withdraw itself entirely within the tube. Locomotor Organs. While, as mentioned above, several genera or individual species present long spines, these become movable, and may be spoken of as appendages, in two genera only. In Polyarthra (fig. 1, E, F) there are four groups of processes or plumes placed at the sides of FIG. 2. Floscularia appendiculata. A and B represent the same animal, some of the organs being shown in one figure and some in the other, oc, eye-spots ; g, nerve ganglion ; p, pharynx (the mouth should be shown opening opposite the letter); ma, the mastax ; e, oesophagus; st, s:omach; a, anus, opening the cloaca; g!, mucous glands in the pseudopodium ; n, nephridia; /, flame-cells; W, contractile vesicle ; m, m, muscles. the body, each of which groups can be separately moved up and down by means of muscular fibres attached to their bases, which project into the body. The processes them- selves are unjointed and rigid. In Pedalion (fig. 3), a remarkable form discovered by Dr C. J. Hudson in 1871 (12, 13, 14, and 15), and found in numbers several times since, these appendages have acquired a new and quite special development. They are six in number. The largest is placed ventrally at some distance below the mouth. Its free extremity is a plumose fan-like expansion (fig. 3, A, a, and H). It is (in common with the others) a hollow process into which run two pairs of broad, coarsely trans- versely striated muscles. Each pair has a single insertion on the inner wall the one pair near the free extremity of the limb, the other near its attachment ; the bands run up, one of each pair on each side and run right round the body forming an incomplete muscular girdle, the ends approximating in the median dorsal line. Below this point springs the large median dorsal limb, which termin- ates in groups of long setas. It presents a single pair of muscles attached along its inner wall which run up and form a muscular girdle round the body in its posterior third. On each side is attached a superior dorso-lateral and an inferior ventro-lateral appendage, each with a fan- like plumose termination consisting of compound hairs, found elsewhere only among the Crustacea ; each of these is moved by muscles running upwards towards the neck and arising immediately under the trochaldisk, the inferior ventro-lateral pair also presenting muscles which form a girdle in the hind region of the body. Various other muscles are present : there are two complete girdles in the neck region immediately behind the mouth ; there are also muscles which move the hinder region of the body. In addition to these the body presents various processes which are perhaps some of them unrepresented in other Rotifers. In the median dorsal line immediately below the trochal disk there is a short conical process presenting a pair of muscles which render it capable of slight move- ment. From a recess at the extremity of this process spring a group of long setose hairs the bases of which are connected with a filament probably nervous in nature. This doubtless represents a structure found in many Rotifers, and variously known as the "calcar," "siphon," " tentaculum," or "antenna." This calcar is double in Tubicolaria and Melicerta. It is very well developed in the genera Rotifer, Philodina, and others, and is, when so developed, slightly retractile. It appears to be repre- sented in many forms by a pit or depression set with hairs. The calcar has been considered both as an intromittent organ and a respiratory tube for the admission of water. It is now, however, universally considered to be sensory in nature. Various forms present processes in other parts FIG. 3. Pedalion mira. A, Lateral surface view of an adult female : a, median ventral appendage; 6, median dorsal appendage; c, inferior ventro-lateral appendage : d, superior dorso-lateral appendage ; /, dorsal sense-organ (calcar) ; jr, " chin ; " x, cophalotroch. B, lateral view, showing the viscera : oc, eye- spots ; n, nephridia; e, ciliated processes, probably serving for attachment; other letters as above. C, ventral view: x', cephalotroch; x, branchiotroch; other letters as above. D, ventral view, showing the musculature (cf. text). E, dorsal view of a male : o, lateral appendages ; 6, dorsal appendage. K, lateral view of a male. G, enlarged view of the sense-organ marked/. H, enlarged view of the median ventral appendage. (All after Hudson.) of the body which have doubtless a similar function, e.g., Microcodon (fig. 1, D, s) with its pair of lateral organs. Pedalion presents a pair of ciliated processes in the posterior region of the body (fig. 3, B, c, and D, e), which it can apparently use as a means of attachment; Dr Hudson states that he has seen it anchored by these and swimming round and round in a circle. They possibly re-