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The digestive system includes the mouth, pharynx, oesoph- 

 agus, ventriculus or stomach, intestine, and rectum. The 

 mouth leads into a not well marked off region, called the 

 pharynx, which is sometimes broader than the oesophagus. 

 The posterior end of the (esophagus is generally enlarged, form- 

 ing the ingluves just in front of the stomach. The ventriculus, 

 or stomach, is very large, and its outline can often be seen 

 through the integument of light-colored species or in specimens 

 which have recently emerged from the nymphal skin. 1 have 

 found that treatment with acetic acid and mounting in glycer- 

 ine will frequently show the internal organs very plainly. The 

 stomach is almost like a spherical bag in most cases, with 

 its anterior wall lying at the division between the cephaio- 

 thorax and abdomen, while its posterior wall extends to a point 

 almost above the anal opening. Extending out from the 

 stomach on each side at the posterior part is a blind pouch or 

 ccecum. The cceca vary somewhat in size, shape, and situation 

 with the species. The intestine and rectum are very short and 

 often resemble a C-shaped tube, leading from the posterior wall 

 of the stomach to the anus. In connection with the digestive 

 process is a small pair of glands situated on the front wall of 

 the ventriculus or stomach. 



The tracheal system exists only in the adult forms and is 

 absent in the Hoplodermi dee. The tracheae usually consist of 

 from eight to twelve main trunks, which start from the acetab- 

 ula of the legs, most of them extending backwards in a wavy 

 course to the posterior end of the abdomen, where they become 

 slightly enlarged at their termination to form air-sacs. The 

 trachea 1 are always un branched. 



The nervous system has not been well worked out in the 

 case' of the Oribatoidea but consists of a sub- and a supra- 

 oesophageal ganglion, which have nerves running to the 

 important organs. 



Situated on the sides of the abdominal cavity in the case 

 of some species, is a small sac which opens to the exterior 

 through the integument. This apparatus is supposed to have 

 an excretory function. The region of the cephalothorax is 

 largely occupied by muscles controlling the legs and the mouth- 



