146 THE ROTATORIA. fi 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 liectum 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 faeces, but also of the contents of 

 the genital organs and of the a(iuiferous 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 tcntaculifm-m, rouitory organs oi Stf.phaiio- size throughout, except the rectum wliich is dilated. 



ceros, are also used for the seizure of food -^ see Hut it is coiled, esiiecially with those which are 



£hrenberg, Aliliaudl. d. Berl. Akad. 1832, Taf. enclosed in a carapace, as with Tubicolaria, and 



XI. fig. 1, e., also, Die lufusionsthierchen, Taf. Melicerta, since here the anus is far in front. 



XLV. fig. XI. 5. i" These two pancreatic caeca are nearly always 



'■i For the structure of the teeth, see Ehrenberg, present, being wanting only with some si)ecies of 



Abhand, d. Herl. Akad. 1831, p. 46, Taf. III. IV. Ichthijdium. With JSutummata clavulata, and 



'■'j P/f:iiri)lrocha, Furcularia, and many species Diglena lacuKtris, there are, besides these caeca 



of Tiotiimiiuitu, iunl Diglena. which are long, attached to the stomach many 



4 Uydalina, Euchlanis, Salpina, Anuraea, smaller sacs, which are colorless and perhaps of 



Bracfiionus, and many sijecies of Nolommata, the same nature, 



iind Ijiglena. With Meealotrocha albo-flavicans, there are 



a J'/iiloUma, Lacinularia, Melicerta, and also two like caecal ajipetidages entering the base 



Covockilus. of the stomach, and which are independent of the 



6 With Euchlanis, and Brachionvs, the stem- Bhort pancreatic ones of the same locality ; see 



ach is separated from the intestine by a constric- Elirenbers, Abhandl. d. lierl. Akad. 1S31, Taf. 



tion, and with I'liiludina, the intestine is of equal 111. and, Die lufusionsthierchen, Taf. L. LIV. 



