TARDIGRADA. 857 



spicuous nuclei are placed in each cell in a corresponding position 

 to that of the corresponding cell of the other side of the body. 

 At the end of the limbs and around the orifices into the body 

 the cells are heaped up, but elsewhere the cuticle and the single- 

 layered epidermis surround a spacious body-cavity. This 

 cavity contains the viscera which are bathed by an uncoagu- 

 lable fluid. Numerous corpuscles, increasing in number as the 

 animal grows old, float in this fluid and these in well-nourished 

 individuals are packed with food reserves. The body-cavity is 

 traversed both by muscle-fibres and by nerves symmetrically 

 placed, and the curious absence of connective tissue, associated 

 in many cases with the great transparency of the tissues, allows 

 these to be readily investigated. There are also ventral, dorsal, 

 and lateral bands of muscles, and others that move the limbs 

 and teeth. 



The mouth commences with what is termed the oral cavity, 

 which may or may not be surrounded by certain cuticular rings ; 

 this opens behind into a narrow tube lined by chitin, the mouth 

 tube. The two chitinous teeth or stylets project into the mouth 

 tube in certain species of Macrobiotus and Doyeria but into the 

 oral cavity in Echiniscus, Milnesium and some species of Macro- 

 biotus. These teeth or stylets may be strengthened by a cal- 

 careous deposit. They are moved by three muscles attached to 

 their hinder ends. The mouth-tube passes into a stout muscular 

 pharynx, circular in outline with radiating muscle-fibres. When 

 these contract the lumen is enlarged and the fluid food rusually 

 the cell-sap of some moss cell w r hich has been pierced by the 

 stylets is drawn in. Tw r o glands, called salivary, open into the 

 mouth ; in some species their secretion is considered poisonous. 

 The pharynx is succeeded by an oesophagus which may be 

 reduced to almost nothing ; this opens into a capacious stomach 

 whose walls consist of a layer of very definitely hexagonal cells. 

 Posteriorly this passes into a rectum, which unites with the 

 duct of the excretory organs and of the reproductive organs ; 

 the resulting cloaca opens by a transverse slit between the last 

 pair of legs. 



The excretory function is said to be carried out by a pair of 

 lateral caeca which open into the rectum. These recall the some- 

 what similar diverticula of certain mites and probably represent 

 malpighian tubules. 



