90 



R O T I F E R A 



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 



Fio. 2.FloscutaHa 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, stomach; a, anus, opening the 

 cloaca; gl, mucous glands in the pseudopodium ; n, nephridia; /. flame-cells; 

 bl, 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 setrc. 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 trochal disk, 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; b, median dorsal appendage; c, inferior ventro-lateral 

 appendage : d, superior dorso-lateral appendage ; /, dorsal sense-organ (calcar) ; 

 j7, "chin;" x, cephalotroch. B, lateral view, showing the viscera: oc, eye- 

 spots; ?i, nephridia; e, ciliated processes, probably serving for attachment; 

 other letters as above. C, ventral view: x', cephalotroch; r, brancliiotroch; 

 other letters as above. D, ventral view, showing the musculature (</. text). 

 E, dorsal view of a male : a, lateral appendages ; 6, dorsal appendage. F, 

 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, *) 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- 



