70 BRITISH TYEOGLYPHID^]. 



look continuous ; the oesophagus appearing to commence 

 at a slightly lower level than that at which the 

 pharynx terminates; although the continuity of the 

 lumen is seen immediately these passages are at all 

 distended. The oesophagus passes right through the 

 centre of the so-called brain, as is usually the case in 

 the Acarina. There is only a very short portion of 

 the organ anterior to the cerebral mass in the Tyro- 

 glyphidae whose anatomy is known to me, far shorter 

 than is the case in Trombidium, Bdella, Thy as, etc., 

 but the lumen is much larger. In the genera named 

 the opening in the brain for the passage of the oeso- 

 phagus is very small, scarcely larger than the diameter 

 of the thin tube of the oesophagus when not occupied 

 by food; in the Tyroglyphidas it is greatly wider 

 (PL A, figs. 9, 12; PL C, fig. 1), and the oesophagus 

 when empty does not nearly fill it. This also is 

 similar to what occurs in the Oribatida3 ; doubtless for 

 the same reason as the similarity of the occlusor 

 muscles, viz. that solid food is swallowed by both 

 families. 



A short portion of the oesophagus usually lies behind 

 the brain (PL A, figs. 1, 10) ; at its posterior end this 

 often widens out somewhat, and sometimes is slightly 

 invaginated, and protrudes a little into the ventriculus ; 

 this was noticed by Kalepa in Tyroglyphus longior, 

 and I have seen a similar arrangement in some 

 Oribatidse ; it serves to prevent the regurgitation of 

 food from the ventriculus into the oesophagus, which 

 is also hindered in some cases by a ring muscle. 



The Ventriculus (PL A, figs. 1,2; PL C, fig. 1, v) is 

 the largest viscus in the alimentary canal ; it is doubt- 

 less the great seat of digestion. In Gflycyphagus platy- 

 g aster it is a large sack with thick walls, and having a 

 somewhat triangular form with the base of the triangle 

 at the posterior end and the oesophagus entering at 

 the anterior point ; the posterior corners are strongly 

 rounded; a somewhat similar form is described by 

 Nalepa for Tyroglyphus longior. G-udden does not 



