146 $ 186. 
THE ROTATORIA. 
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 unidentate 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 faeces, 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 tentaculiform, rotatory organs of Stephano- 
ceros, are also used for the seizure of food; see 
Ehrenberg, Abhandl. d. Berl. Akad. 1832, Taf. 
XI. fig. 1, e., also, Die Infusionsthierchen, Taf. 
XLV. fig. II. 5. 
2 For the structure of the teeth, see Ehrenberg, 
Abhand. d. Berl, Akad. 1831, p. 46, Taf. ITI. IV. 
3 Pleurotrocha, Furcularia, and many species 
of Notommata, and Diglena. 
4 Hydatina, Euchlanis, Salpina, Anuraea, 
Brachionys, and many species of Notommata, 
and Diglena. 
5 Philodina, 
Conochilus. 
6 With Euchlanis, and Brachionus, the stom- 
ach is separated from the intestine by a constric- 
tion, and with Philodina, the intestine is of equal 
Lacinularia, Melicerta, and 
size throughout, except the rectum which is dilated. 
But it is coiled, especially with those which are 
enclosed in a carapace, as with Tubicolaria, and 
Melicerta, since here the anus is far in front. 
7 These two pancreatic caeca are nearly always 
present, being wanting only with some species of 
Ichthydium. With Notommata clavulata, and 
Diglena lacustris, there are, besides these caeca 
which are Yong, attached to the stomach many 
smaller sacs, which are colorless and perhaps of 
the same nature. 
With Megalotrocha albo-flavicans, there are 
also two like caecal appendages entering the base 
of the stomach, and which are independent of the 
short pancreatic ones of the same locality ; see 
Ehrenberg, Abhandl. d. Berl. Akad. 1831, Taf. 
II. and, Die Infusionsthierchen, Taf. L. LIV. 
