146 TUE ROTATORIA. § 136. 



dilatation. This dilatation is continuous into an intestine which opens exter- 

 nally by an anus. 



The mouth is always between the rotatory organs, so that it receives 

 what is drawn in by their vortical action, — the animal swallowing or re- 

 jecting the particles at will."> 



The pharyngeal masticatory apparatus is round, and composed of two 

 jaws having one or several teeth, which are brought together laterally by 

 the action of special muscles.'-' 



Usually these jaws are formed of two knee-shaped divisions [Processus 

 anterior and posterior). The posterior division gives insertion to the masti- 

 catory muscles, but the anterior terminates with a tooth,'''' or as a multi- 

 dentate apophysis.'^' With some which have this last arrangement,'^* the 

 two jaws are formed of three horny arches, and noted for their stirrup-like 

 form. Two of these arches [Arcus superior and inferior), form the arched 

 portion of the stirrup, pointing inwards, while its base is formed by the 

 third arch [Arcus externus), pointing outwards. The masticatory muscles 

 are inserted upon the inferior arch, and move against each other — the 

 transversely-arranged teeth passing over the other two. 



With the multidentate Monotrocha, and Zygotrocha, the pharynx rests 

 always in the same locality ; but with the uuidentate Polytrocha, it can 

 move up and down, and even be protruded through the mouth. In this 

 last case, the teeth serve as pincers for the seizure of food. The intestine 

 usually traverses the cavity of the body in a straight line, rarely loop- 

 ing,'*^' and is lined throughout with ciliated epithelium. 



From the stomachal dilatation to a point near the anus, its walls are 

 very thick. The walls of the stomach and intestine are formed of large 

 cells with a colorless nucleus, and which, as they contain a brownish or 

 greenish granular substance, are of an hepatic nature. 



With most species, two caeca, rarely more, with thick walls and lined 

 with ciliated epithelium, open on the right and left of the beginning of the 

 stomach. Their walls are also composed of large cells, which, as they 

 differ widely from the hepatic ones by their colorless contents, may perhaps 

 serve the function of salivary glands or pancreas. ''^' 



The term Rectum has been given to a short and terminal portion of the 

 intestine, which has thin walls, capable of being widely distended by faeces. 

 Its orifice is excretory not only of the faaces, but also of the contents of 

 the genital organs and of the aquiferous system — and may therefore be 

 regarded as a cloacal as well as an anal opening. It is nearly always at 

 the base of the caudal extremity. 



1 The tentacuUform, rotatm-y organs of Stephana- size throughout, except the rectum which is dilated. 

 eeros, are also used for the seizure of food ; see But it is coiled, especially with those wliich are 

 Khrenberg, Abhnnai. d. Berl. Akad. 1832, Taf. enclosed in a carapace, as with Tubicolaria, and 

 XI. fig. 1, e., also, Die Infusionsthierchen, Taf. Me/icerta, since here the anus is far in front. 

 XLV. fig. II. 5. 7 These two pancreatic caeca are nearly always 



2 For the structure of the teeth, see Ehrenbf.rg, present, being wanting only with some species of 

 Abhand. d. lierl. Akad. 1831, p. -lii, Taf. III. IV. Ichthydium. With ISotommata clavulnta, and 



3 P/eurotroclia, h'urcularia, and many species Disleita Iac7(xtris, there ;ire, besides these caeca 

 of Tiotommata, and Diglena. which are long, attached to the stomach many 



* Hydatina, Euchlnnis, Sa/pina, Anuraea, smaller sacs, which are colorless and perhaps of 



Bractiionus, and many species of Notommata, the same nature. 



and Vifflena. With Megalotrocha albo-flavicans, there are 



^ Phi/odina, Lacinularia, Melicerta, and also two Uke caecal ai)pendages entering the base 



Conochilus. of the stomach, and wliich are independent of the 



6 With Euchlanis, and Brnckionus, the stom- short pancreatic oms of the same locality ; see 



ach is separated from the intestine by a constric- Ehrenberg, Abhandl. d. lierl. Akad. 1831, Taf. 



tion, and with Phiiodina, the intestine is of equal HI. and. Die Infusionsthierchen, Taf. L. LIV. 



