XIx ANATOMY 481 
supported by a second chitinous tooth-bearer,’ and the movement 
of each is controlled by three muscles, one of which, running 
forwards to the mouth, helps to protrude the tooth, whilst the 
other two running upwards and downwards to the sheath of 
the pharynx, direct in what plane the tooth shall be moved. 
The mouth-tube passes suddenly into the muscular sucking 
pharynx, which is pierced by a continuation of its chitinous tube. 
Roughly speaking, the pharynx is spherical ; the great thickness of 
its walls is due to radially arranged muscles which run from the 
chitinous tube to a surrounding membrane. When the muscles 
cortract, the lumen of the tube is enlarged, and food, for 
the most part liquid, is sucked in. Two large ‘glands, composed 
of cells with conspicuous nuclei, but with ill-defined cell out- 
lines, pour their contents into the mouth in close proximity to 
the exit of the teeth. The secretion of the glands—often termed 
salivary glands—is said in many cases to be poisonous. 
The pharynx may be followed by a distinct oesophagus, 
or it may pass alinost immediately into the stomach, which con- 
sists of a layer of six-sided cells arranged in very definite rows. 
In fully-fed specimens these cells project into the lumen with a 
well-rounded contour. Posteriorly the stomach contracts and 
passes into the narrow rectum, which receives anteriorly the 
products of the excretory canals and the reproductive organs, and 
thus forms a cloaca. Its transversely-placed orifice les between 
the last pair of legs. The food of Tardigrades is mainly the sap 
of mosses and other humble plants, the cell-walls of which are 
pierced by the teeth of the little creatures. 
The organs to which an excretory function has been attributed 
are a pair of lateral caeca, which vary much in size according as 
the possessor is well or ill nourished. They recall the Malpighian 
tubules of such Mites as Tyroglyphus. Nothing comparable in 
structure to nephridia or to coxal glands has been found. 
The muscles show a beautiful symmetry. There are ventral, 
dorsal, and lateral bundles, and others that move the limbs and 
teeth, but the reader must be referred to the works of Basse, 
Doyére,” and Plate® for the details of their arrangement. The 
muscle-fibres are smooth. 
1 A. Basse, Zeitschr. wiss. Zool. \xxx., 1906, p. 259. 
2 Ann. Sct. nat. (2), xiv., 1840, p. 269, and xvii., 1842, p. 193. 
® Zool. Jahrb. Anat. iii., 1889. This paper contains a bibliography. 
VOL. IV 21 
