NO. 1382. 



THE A CARINA OR MITES— BANKS. 



The (esophagus i.s a lono- .siniplo tube; the .stonuieli is of varied size and 

 shape, according- to the t'ood-hal)its. Sometimes there is an enh\rge- 

 ment of the cesophag-us near its end, thus forming- an ingluvies or crop. 

 In some forms the cceca are extremely long or numerous. The Mal- 

 pighian vessels, when present, are two in number, and enter the short 

 intestine near its end. The latter is sometimes provided with an 

 enlargement, the colon. In many mites the digestive system is much 

 simplitied. In many, if not all, of the forms allied to TromhUhun^ 

 and the water-mites, there is no certain connection between the stomach 

 or ventriculus and the anus. The ventriculus ends blindly, the anus 

 opens into a large tu))e, supposed to have an excretor\^ function. 

 Many of these forms feed on animal juices, so probablj' have no 

 excreta. 



Fig. 3. — Palpi of various forms, a, bdella; ft, cheyletus; c, gamasus; rf, scirus; e, histiostoma; 



/, EL'PODES; g, SARCOPTES; /), ARRENURUS; /, TROMBIDU'M. 



The nerve ganglia are united into one mass of considerable size, 

 pierced by a hole for the cesophagus. This brain doubtless is formed 

 of the supra and sub-(esophageal ganglia and their commissures, but 

 so closely are the parts united that all trace of demarcation is com- 

 monly lost. The principal nerves arise from this brain. There is one 

 unpaired nerve, and nine or more pairs of nerves. Three sets of 

 paired nerves and the unpaired one arise from the supra-(jesophageal 

 ganglion and are of small size. The other six or more sets of paired 

 nerves arise from the sub-oesophageal ganglion and are mostly of 

 larger size. The impaired, or medium nerve, goes to the phar3'nx. 

 The paired nerves of the supra- oesophageal gangMon go to the eyes, 

 the mandibles, and the large vertical muscles nQB.. the base of the ros- 

 trum. Of the nerves of the sub-oesophageal ganglion, one pair goes 

 to the palpi, four to the legs, and one to the genital and other abdomi- 



