INTERNAL ANATOMY. 65 



features. The canal of the TyroglyphidaB is far more 

 closely allied to that of the Sarcoptidae and the Oriba- 

 tidaa, and is even more or less similar to that of the 

 Gramasidae ; notwithstanding the far higher organisation 

 of that family in almost all points of its anatomy ; it 

 is, however, decidedly simpler than that of the Grama- 

 sidae or Oribatidaa, as might reasonably be expected. 



The alimentary canal of the Tyroglyphidae, like that 

 of the Oribatidas, lies somewhat loosely in the body 

 cavity ; being firmly attached at the oral and anal ends, 

 but having very little attachment between those points ; 

 although it is slightly supported by a certain amount 

 of connective and fatty tissues. If the oral and anal 

 attachments and the pharyngeal and rectal muscles be 

 cut, the canal may be removed on a hair quite entire ; 

 it was doubtless this slightness of attachment which 

 enabled Gudden to obtain the organs successfully by 

 the curious method which he employed. 



The post-oral alimentary canal in the family which 

 I am dealing with consists of the pharynx ; the oeso- 

 phagus ; the ventriculus, with two large caecal appen- 

 dages ; the colon ; the rectum, terminating in the anus ; 

 and finally of two Malpighian vessels ; which, however, 

 do not appear to be invariably present. 



The Pharynx (PI. A, fig. 5 and figs. 1 and 2, pJi) is 

 the great swallowing, or sucking, organ in all Acarina 

 of which w^e know the anatomy ; it commences at the 

 posterior end of the oral chamber. Haller * says that 

 in Tyroglyphus it is encircled by a chitinous ring 

 where it joins the mouth-cavity, but I have not been 

 able to detect this nor have I found it drawn or 

 described by any other author ; its presence would be 

 somewhat unexpected, as it would apparently be likely 

 to interfere with the great function of the pharynx ; as 

 the pharynx does not join the mouth in a direct 

 perpendicular plane, but rather in a curved and 

 diagonal loop. 



* " Zur Kenntniss der Tyroglyphen und Verwandten," in ' Zeit. 

 wiss. Zool.,' Bd. xxxiv, p. 276, Taf. ix, fig. 16, I. 



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