410 GENEEAL HISTOBY OF THE INFTJSOKIA. 



within the body ; the body itself may be extended at full length, or very 

 much contracted on itself. So much may the whole animal be contracted, 

 that, except by the detection of the characteristic Rotatorial organization, its 

 nature would certainly be mistaken. An illustration of this is furnished in 

 the figures of Dujardin and Perty (XXYIII. 4). 



The mode of termination of the pseudopodium permits many of the Rota- 

 toria to attach themselves at will to any object, some (Pterodina, for in- 

 stance) assuming a fijced position for a long time together. "When thus at 

 rest, the rotaiy organ may be retracted or extended ; in the latter case, al- 

 though suspending its function as an organ of locomotion, it is in full operation 

 as a respii'atory organ, as well as sei^ving to procure food. The body, more- 

 over, is often in active motion when fixed by the extremity of the foot-process 

 — oscillating fi'om side to side, bending itself, and even turning as on a pivot. 



The Digestive System. — The Rotatoria possess a distinct and undoubted 

 alimentary canal, evident as a tube, traversing the interior, from a mouth to 

 a posterior outlet or anus, composed of distinguishable parts "svith accessory 

 organs. One group of the family is deficient of the anal outlet ; and in male 

 animals the digestive apparatus is atrophied or wanting. 



The digestive tube is mostly straight throughout its coui'se (XXXIX. 1 ; 

 XL. 1) ; the exceptions to the rule occur with the encased genera, in which 

 the intestine is curved on itself, and the anus advanced forwards to some spot 

 beneath the head (XXXVII. 17 i). 



The parts to be distinguished in the alimentary canal are — 1st, the mouth 

 or oral cavity ; 2nd, the pharynx or vestibule (XXXYII. 19 a) between the 

 1st and 3rd, the oesophageal head (XXXYII. 19 6) ; 4, the stomach, with 

 appendages (XXXYII. c, d) ; 5, the intestine with its outlet ; and 6, the 

 cloaca (XXXYII. e,f). Each and aU of these parts present great diversity 

 in figure, size, and accessory organs ; but yet in nearly aU forms the peculiar 

 type of the digestive canal of Rotatoria is well marked. 



The mouth is situated, as a rule, on the margin of the trochal disk, at 

 the centre of its ventral aspect. "Wliere the circlet of cilia is double, as in 

 Lacimdaria and Melicerta (XXXYIII. 21), the mouth, as we have already 

 seen, is placed between the two rows ; and in Floscularia and Stephanoceros 

 it occupies the centre of the area formed by the ciliated apparatus of the 

 head. The mouth is, moreover, subject to variations from the presence of 

 appendages about it. Thus, in Melicerta, Prof. Williamson describes two small, 

 projecting, " flattened lobes with ciliated margins, continuous with those of 

 the ' chin,' which obviously assist in dii-ecting the food into the oesophagus." 

 Leydig notices, in Notommata Sieboldii, a sort of upper Up, not ciliated ; and 

 Huxley, in Lacimdaria, states that the mouth is vertically elongated, and its 

 cavity expanded into " two lateral pouches, which give it an obcordate form ; 

 these lateral pouches contain the lateral ciliated arches that become lost 

 below in the cilia of the pharynx." In Floscidaria the cavity of the mouth 

 is funnel-shaped (infiindibuliform) (woodcut), and is termed by Dr. Dobie the 

 *' infundibulum," who describes the edge to be ''frequently divided into 

 lobes." ^ , 



The mouth opens posteriorly into a canal, through which the food passes 

 to reach the " oesophageal bulb." This canal has unfortunately received 

 various names, viz. cesophagus, pharynx, vestibule, infundihidum, and ''buccal 

 funnel." The fii'st term has likewise been applied to another tube intervening 

 between the " (esophageal head " and the stomach ; hence a looseness of no- 

 menclature, tending to confusion and error in description. If, as is usually 

 done, the name " oesophageal hulh " be given to the jaws and their muscular 

 envelope, then that of oesophagus rightly belongs to the canal leading thence 



