INTERNAL ANATOMY. 69 



the absence of any description on the point, I am not 

 certain that this is his intention. 



There is not any approach to the extremely diagonal 

 levator tecti pharyngw muscles found, e. y., in Bdella ; 

 this doubtless is a consequence of the far shorter 

 rostrum of the Tyroglyphidse. 



The levator tecti pharyngis muscles in the Tyrogly- 

 phidae whose anatomy I have studied are not attached 

 to the roof of the pharynx by tendons which I could 

 detect, as is the case in other families which I have 

 investigated, and Nalepa does not draw or mention 

 any such tendons ; therefore we must at present con- 

 clude that they do not usually occur in the family. It 

 may possibly be that as there are not transverse 

 occlusor muscles passing between each levator muscle 

 and its anterior neighbour, as in the other families 

 spoken of, open space between the levatores is not so 

 important. 



It is probably in the occlusor muscles of the pharynx 

 (m op) that the greatest departure from the type given 

 above exists. Instead of these consisting wholly of 

 straight transverse muscles passing from one lateral 

 edge of the half-tubes to the opposite edge (PI. C, 

 fig. 9, mop), the Tyroglyphidae known to me have 

 only a few such muscles at the hind part of the 

 pharynx, which is constricted principally by ring 

 muscles passing round it ; this may be seen clearly in 

 dissections (PL A, fig. 2), and is similar to the arrange- 

 ment in the Oribatidse. The reason for this would 

 appear to be that the members of both these families 

 live upon solid food, not upon fluids like Bdella and 

 Trombidium, and therefore the pharynx requires to be 

 capable of much greater expansion and contraction. 



The (Esophagus (PL A, figs. 1, 10, on) where it 

 joins the pharynx turns suddenly backward and slightly 

 downward, forming almost an angle with that organ ; 

 at this point the lumen is very narrow when not dis- 

 tended. The effect of this is that in sagittal (longi- 

 tudinal) section the two organs when at rest hardly 



