74 OENEBAL HTSTOBY OF 



by the action of the curious rotary organ, (described in the last 

 section) wbicb surrounds that opening. It, first of all, enters a short 

 cavity, known as ' the crop,' and is then submitted to the action of 

 homy jaws, mostly armed with teeth, and enclosed in a powerful 

 muscular apparatus, forming what is called the oesophageal head, 

 or bulb Separate drawings of this bulb, with the different arrange- 

 ment of the teeth, are shewn in figures 377, 382, 383, 396, 420, 

 424, 433, 437, 444, 455, and 456. It next passes thi'ough a canal, 

 the oesophagus, into a dilated space, termed the stomach, and, after 

 due digestion, is propelled thence, through an intestine, to the 

 outlet. 



The whole course of the alimentary canal is mostly straight, but, 

 in some Rotatoria, for instance, in Tubicolaria and Melicerta, it 

 presents a slight coil. The canal is Hned by vibratile cilia, which 

 assist in the introduction and propulsion of food. 



The portion of the alimentary tube, immediately posterior to the 

 mouth, is funnel-shaped, and hence, called by Dr. Dobie, the infun- 

 dihulum, having its edge frequently divided into lobes, (see fig. .) 

 This space is separated by a rim, armed by non- vibratile cOia, from 

 the next portion, called, by M. Dujardin, \hQ vestibule ; and which 

 leads into a very dilatable cavity, called the crop, a fissured partition, 

 or diaphragm, intervening between the two. The crop ends below, 

 in, or in some measure, contains the oesophageal bulb, with its usual 

 armature of teeth, supported on horny jaws, and separable by 

 pressure. 



This manducatory, or chewing apparatus, has been compared to 

 the gizzard of birds, which it resembles in function, but is, otherwise, 

 more like the crushing toothed apparatus, in the stomach of crabs, 

 lobsters, &c. The number, form, and arrangement of the teeth, 

 afford excellent characters for the systematist ; and will be found 

 figured, in the case of many genera, as referred to above. 



In most instances, the oesophageal bulb, although enjoying con- 

 siderable latitude of motion within the body, does not project from 

 it; but, in some single-toothed forms, ox-JBrachiontis, with the 

 rotary organ divided, this bulb protrudes beyond the mouth, and 

 thus becomes a prehensile organ, using its teeth like claws or 

 pincers. 



