156 



MANUAL OF ZOOLOGY. 



In Chcetoiwtus, and one or two other forms, there is no true 

 wheel-organ, capable of protrusion and retraction, bat the cilia 

 are variously disposed over the surface of the body. 



The proximal extremity of the body in the free forms termi- 

 nates in a caudal process, or * foot,' sometimes telescopic, which 

 ends in a suctorial disc, or in a pair of diverging ' toes,' which 

 act as a pair of forceps. 



The mouth usually opens into a pharynx, or ' buccal funnel,* 

 which is generally provided with a muscular coat, constituting 

 the 'mastax,' or 'pharyngeal bulb,' and which generally con- 

 tains a very complicated masticatory apparatus.* The parts 

 of this apparatus are horny, and are believed by Mr. Gosse to 

 be homologous with the parts of the mouth in Insects. In the 

 females of almost all known species of Rottfera the intestinal 

 canal is a more or less simple tube, extending through a well 

 developed perivisceral cavity, and terminating posteriorly in 

 a dilation, or ' cloaca,' which forms the common outlet for the 

 digestive, generative, and water- vascular systems. 



In both sexes there is a well developed water-vascular 

 system, usually consisting of the following parts: In the 

 hinder part of the body, close to the cloaca, and opening into 

 it, is a sac or vesicle, which is termed the ' contractile bladder,' 

 and exhibits rhythmical contractions and dilatations. From 

 the contractile bladder proceed two tubes the 'respiratory 

 tubes' which pass forwards along the sides of the body, and 

 terminate anteriorly in a manner not quite ascertained. At- 

 tached to the sides of the respiratory tubes, in all the larger 

 Rotifera, is a series of ovate or pyriform vesicles, each of which 

 is furnished internally with a single central cilium, which is 

 fixed to the free end of the vesicle. The exact function of this 

 water- vascular system is not known, but it is most probably 

 respiratory and excretory. Dr. Leydig believes that water 

 enters the perivisceral cavity by endosmose, where it mingles 

 with the absorbed products of digestion, to form the so-called 

 ' chylaqueous fluid ; ' and that the effete fluid is excreted by 

 the respiratory tubes, and ultimately discharged into the 

 cloaca by the contractile bladder. Taking this view of the 

 subject, Mr. Gosse believes that ' the respiratory tubes repre- 

 sent the kidneys, and that the bladder is a true urinary 

 bladder ; ' and consequently that ' the respiratory and urinary 

 functions are in the closest relation with one another.' This 

 observer, further, finds a decided analogy between the above 



* The lower jaws, or ' incus,' consist of a fixed portion, the ' fulcrum,' to 

 which are attached two movable blades the 'rami.' The upper jaws, or 

 ' mallei,' consist each of a handle, or ' manubrium,' to which is hinged a 

 toothed blade, or ' uncus.' 



