28 Acarology 



there was no opening into the hind-gut from the ventriculus. Blauvelt 

 1945 has demonstrated such an opening in a Tetranychus (Figure 27). 

 The sarcoptiform type is more nearly Hke the parasitiform than the 

 trombidiform. All of the divisions — pharynx, esophagus, ventriculus, 

 intestine, colon, and rectum — are usually distinguishable. The body of 

 the ventriculus is usually larger than its pair of posterior caeca. In this 

 respect it differs widely from the mesostigmatid type. 



Figure 21 A longitudinal section through the body of a Tetranychus. (After 

 Blauvelt 1945) 



A number of salivary glands empty on the gnathosoma near the 

 mouth. These glands probably produce secretions which contain diges- 

 tive enzymes. The larvae of many of the Trombidiformes can digest 

 the cuticle of their hosts. In the spider mites certain of the glands pro- 

 duce silk. The cells of the epithelial wall of the ventriculus and its caeca 

 are glandular. They probably secrete digestive enzymes and it is prob- 

 able that digestion and absorption occur principally in the lumen and 

 cells of the mid-gut. The feces are formed in the intestine and are 

 usually voided with the excretory products as tiny spheres. A secretion 

 is used by the deutonymphs of certain uropodids to form an anal 

 pedicel by which they attach themselves to larger arthropods, usually 

 beetles. 



Excretory System: Three types of excretory organs are found in the 

 Acarina. The most primitive is the coxal gland. Excretory tubules that 

 open into the hind-gut but which are endodermal in origin are the most 

 usual type. As previously mentioned the hind-gut of the Trombidi- 

 formes becomes modified to form an excretory organ. In addition to 

 these organs, the cells of the mid-gut are excretory in function. During 

 digestion the cells become filled with excretory products that are cast 



