36 INVERTEBRATE ZOOLOGY. 



Order 7. Acarina Abdomen fused with cephalo-thorax. 



Body unsegmented. Appendages about 

 mouth often modified to form a sucking 

 tube. Respiration by tracheal tubes or 

 merely through integument in smaller 

 forms — many parasitic. 

 if Ixodes, Tyroglyphus. 



SUPPLEMENTARY GROUPS. 



Pantapoda Extremely atteniiated marine forms with 



long slender legs and body of aboiit the 

 same diameter. Cephalo-thorax of six 

 segments, of which the first are fused, 

 possessing a beak at the anterior end. 

 Abdomen much reduced and sac-like. 

 Seven pairs of legs, containing the repro- 

 ductive organs and diverticula of the 

 stomach. Respiratory organs fail. 

 ■if Nymphon, 



Tardigrada Minute fresh water forms, with four 



pairs of short legs bearing little hooks. 

 Hermaphroditic — without heart or organs 

 of respiration, if Macrobiotus. 



Pentastomidea (Linguatulina) Parasites in the lungs and nasal cavities 



of reptiles and mammals. Long, flat- 

 tened worms, resembling Taeniae, but 

 with Arachnoid development. Legs re- 

 duced to two pairs of hooks about the 

 mouth, if Pentasstomum. 



Class III. Tracheata Antennata. . .Head always distinct, never fused 



with thorax, one pair of antennae, breathe 

 by system of tracheal tubes opening bj' 

 stigmata. 



