68 BRITISH TYROGLYPHID^E. 



where they join ; when these muscles contract the 

 edges of the half -tubes are brought nearer together; 

 consequently the upper and inner half-tube is driven 

 down upon the lower and outer one. This alternate 

 action is the sucking process. 



This type is a good deal departed from in Gamasus, 

 where the lumen of the pharynx when very slightly 

 distended is triradiate in the species which I have cut 

 sections of, and the distensor muscles are inserted into 

 the lateral as well as the superior walls of the organ ; 

 but the principle is similar. 



The pharynx in the Tyroglyphida3, or at least in 

 those species of that family whose pharyngeal anatomy 

 has been investigated, does not depart greatly from the 

 type above described ; but it is probably the simplest 

 form of that type known, as might naturally be anti- 

 cipated. In Glycyphagus platygaster the distensor 

 phari/ngis muscles consist of, I think, five pairs of 

 muscles (PL A, fig. 5, mlp) placed in two longitudinal 

 rows, one on each side of the median line. The second 

 and anterior muscles are the longest, the length 

 diminishing gradually in the third to fifth pairs. This 

 arises chiefly from the strong upward turn which the 

 pharynx takes as it passes backward. The central 

 pair of muscles are almost perpendicular ; those in 

 front and behind radiate slightly, so as to raise the 

 whole roof of the pharynx (pr) 9 which is somewhat 

 longer than the roof of the rostrum (rr), being the 

 outer of the two more or less concentric curves. The 

 levator ipcti phari/ngis (distens&r) muscles of Hericia 

 Robini are similar (PL C, fig. 1), but Nalepa, treating 

 of those of Tyroglyphus longior, although he does not 

 say how many pairs there are, says that they are 

 numerous ; but then he seems to me to draw four or 

 five pairs wholly contained within the same transverse 

 perpendicular plane,* an arrangement which I have 

 not seen. But Nalepa's drawing is very small, and in 



* Nalepa, ' Abtli. i,' Taf. 1, fig. i. 



