30 Acarology 



The Mesostigmata and Ixodides have a single pair of stigmata in the 

 aduhs, but in larval ticks there may be found several pairs of stigmata. 

 The stigmata open into an atrium from which the tracheal trunks arise. 

 Associated with the stigmata and trachea there is a chitinous tube, the 

 peritreme. In the Mesostigmata the stigmata are situated ventrally lat- 

 eral to the coxae and at the level of or in front of coxae in. The peri- 

 tremes are usually long and anteriorly directed. They may be extended 

 posteriorly for some distance as well and they may be almost straight 

 or strongly bent. In the Ixodides the peritreme is never tubelike and is 

 confined to the area adjacent to the stigmata that are placed behind or 

 lateral to coxae iv. 



The stigmata of the Trombidiformes are usually situated on the 

 gnathosoma or between the gnathosoma and the propodosoma. The 

 females of the Tarsonemini have a pair or two pairs of stigmata on 

 the proterosoma. Many males lack a respiratory system entirely. The 

 Prostigmata have the stigmal openings on the gnathosoma and fre- 

 quently stigmal horns or peritremes are present (Figure 28). The peri- 

 tremes of the prostigmatids give rise to tracheal trunks and are not 

 similar to the peritremes of the Mesostigmata. Many of the bdellids 

 have a genital tracheal system in addition to the usual prostigmatic 

 type. In a number of the smaller trombidiform mites stigmata and 

 tracheae are reduced or wanting. 



The Sarcoptiformes lack tracheae and stigmata or have minute 

 tracheae. The Acaridiae lack a specialized respiratory system. Most 

 Oribatei are remarkable in that they have developed a system of 

 tracheae that opens through stigmata and porose areas in many regions 

 of the body. In this group even the pseudostigmata are associated with 

 the respiratory system. Grandjean 1934 describes in detail the struc- 

 ture of the respiratory system of this group. Some of the oribatids, 

 however, lack respiratory openings and tracheae. 



Nervous System: Consolidation of the segmental ganglia has pro- 

 gressed in the Acarina to such an extent that the central nervous sys- 

 tem is an integrated mass surrounding the esophagus. In the embry- 

 onic and larval stages fusion of the ganglia is not as complete as in the 

 nymphs and adults. The portion of the brain dorsal to the esophagus 

 gives rise to the nerves that supply the pharynx, chelicerae, and eyes. 

 The nerves that run to the pedipalps, legs, and posterior internal organs 

 all originate from that portion of the brain that is ventral to the esoph- 

 agus (Figure 29). The nerves that run to the appendages do not sup- 



