pair of appendages, corresponding to the mandibles of insects, are called 

 the chelicerae, the second the pedipalps ; when the second pair has a jaw- 

 like portion, the two may be fused with the second maxillae to form the 

 labio-maxillary dart or hypostome. There are four pairs of legs in the 

 adult. The alimentary canal is straight, and the anus ventral, not termi- 

 nal. Metamorphosis is incomplete, the young generally resembling their 

 parents. 



The blood-sucking forms are confined to one order, the ACARINA, in 

 which the body is soft rather than rigid, is non-articulated, and usually 

 either rounded or oval. The thorax and abdomen are fused together 

 as a rule, though they may be separated by a groove, the anterior 

 portion being spoken of as the capitulum. The mouth parts are adapted 

 for the purpose of attaching the animal to its host while sucking. Re- 

 spiration is carried on by tracheae, the position of the stigmata or respi- 

 ratory openings being important in classification. Metamorphosis is 

 incomplete, the larva resembling the parent, but possessing only three 

 pairs of legs, while the nymph and adult have four. The order is 

 divided by Ray Lankester into seven suborders, only four of which 



concern us. 



Suborder METASTIGMATA. 



Suborder PROSTIGMATA. 



Acarina in which the integument 

 is mostly hard ; a pair of stig- 

 mata is situated above and be- 

 hind the base of the fourth legs. 

 This suborder contains the 

 Gamastdae, and the Ixodidae. 

 It is to these two families that 

 the blood-sucking acari, ticks, 

 and mites belong. (Chapters 

 viii and ix.) 



Acarina in which the stigmata 

 when present lie close to, or 

 above the base of the chelicerae; 

 they are absent in some of the 

 aquatic forms. The integu- 

 ment is soft, but with sclerites; 

 those on the ventral surface 

 apparently represent the proxi- 

 mal segments of the legs em- 

 bedded in the body. This sub- 

 order contains the families 



