THE ACAEIXA OR MITES. 



11 



mites, there is no certain connection between the stomach or ventriciilus and the 

 anus. The ventriciihis ends blindly; the anus opens into a large tube, supposed 

 to have an excretory function. Many of these forms feed on animal juices, so probably 

 have no excreta. 



The nerve ganglia are united into one mass of considerable size, pierced by a hole 

 for the oesophagus. This brain doubtless is formed by the union of the supra- and sub- 

 oesophageal ganglia and their commissures, but so closely are the parts united that all 

 trace of demarcation is commonly 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 supraoesophageal ganglion and are of small 

 size. The other six or more sets of paired nerves arise from the sub oesophageal gang- 

 lion and are mostly of larger size. The unpaired, or median nerve, goes to the phar- 

 ynx. The paired nerves of the supraoesophageal ganglion go to the eyes, the mandi- 

 bles, and the large vertical muscles near the base of the rostrum. Of the nerves of the 

 suboesophageal ganglion, one pair goes to the palpi, four to the legs, and one to the 



Fig. 5.— Anatomy of Parasitus: a, Mandible; b, salivary gland; c, retractor rostrum; d, muscles of man- 

 dibles; e, ventriculus; /, sacculus foemineus; g, lyrate organ; h, ova; i, levator ani; l, fat cells; I, cloaca; 

 m, anus; n, embryo; o, bind gut; p, vagina; s, vulva; t, braia; v, oesophagus; x, pharynx. (Author's 

 illustration.) 



genital and other abdominal organs. Sometimes there are other nerves that extend 

 to the posterior part of the body. 



The reproductive system is often highly developed and frequently occupies a con- 

 siderable part of the body. The testes of the male aie large, lobate, and open into two 

 tubes, tlie vasa deferentia, wliich, uniting to form the ductus ejaculatorius, may open 

 through an extensile penis. The ovaries (sometimes united) are situated in the middle 

 part of the body, are of varying shape, and open into two tubes — the o\iducts — which 

 unite to form the \Tilva. The latter may have a spermatheca attached, and may open 

 through an extensible ovipositor. In some families the A-ulva is not a bursa copulatrix, 

 but there is a special copula tory opening near the anus. In other forms the female 

 organs are very different, as will be mentioned under the families. 



In the Parasitidse, TjToglyphidse, and Oribatidse there are a pair of glands in each 

 side of the abdomen, each opening by a pore in the skin. They contain a yellowish, 

 oily liquid, and are considered excretory glands; Michael has called them "expiilsory 

 vesicles. ' ' In most mites there are several glands in the head region, some of them evi- 

 dently of a salivary nature, but others are often present whose function is unknown. 

 Some of them open into the mouth, or pharynx, and others may open at the base of the 

 mandibles. 



In the Prostigmata, Thor has found as many aa seven kinds of glands, one pair of 

 which are often longer than the entire body. There is also a median unpaired gland 



I 



