THE ACARINA OR MITES— BANKS. 



body; in many conmion forms they open near the mandibles. In 

 ticks and (xamasids they open near the hind legs. In other forms 

 they open in the acetabula or coxal cavities. The openings of the 

 trachciv are through stigmata or spiracles which xnYy in different 

 forms. Common!}' there are one or two main tracheal trunks in each 

 side of the body, each giving off many ])ranches. In some forms there 

 is a short tracheal trunk which at its tip gives rise to a great miml)er 

 of tine long tracheiv. each of which is unbranched. A great many 

 mites, however, have no internal respiratory S3'stem whatever. In 

 these forms the skin is soft, and they absorb oxygen by osmosis through 

 the general surface of the body. 



The muscular svstem of mites varies greatly in the different genera. 

 Strong muscles are attached to the mandibles for extending and mov- 

 ing these organs. Still more powerful ones are attached to the legs, 

 and tiiose for the pharynx and organs of generation are often promi- 



m 



Fig. 5. — ANATOMY OF GAMASIS. «, MANDIBLE; h, SALIVARY GLAND; C, KETRACTOR ROSTRUM; (?, MUS- 

 CLES OF mandibles; e, ventriculus; /, sacculus f<j-:mineus; ij, lyrate organ; /(, ova; i, levator 

 ANi; k, fat cells; I, cloaca; m, anus; n, embryo; o, hind gut; p, vagina; s, vulva; t, brain; 



V. (ESOPHAGUS; .r, PHARYNX. 



nent. There are also muscles connecting various parts of the integu- 

 ment and in some cases one or two pairs attached near the middle of 

 the dorsum. These latter often produce the depressions in the dorsal 

 surface which are commonly found in many of the soft-bodied mites. 



The life histories of mites are extremely varia])le, and will be 

 described under each family. There are typically four stages — egg., 

 larva, nymph, and adult. Many mites, however, liave developed a 

 complicated arrangement of forms that almost obscures this funda- 

 mental simplicity. Most of these additional phases occur during tlie 

 nymphal stage, the growing stage of the acarian. 



Nearly all mites deposit eggs, but there are a few forms known to 

 be viviparous, or at least ovoviviparous. and one, Pedindohlex, brings 

 forth adult males and females. 



The general plan of development is as follows: The agg is usually 



