92 ARTHROPODA. 



GROUP B. ARACHNIDA TRACHEATA. Chiefly terrestrial Arachnidans, 

 with chelicera? (falces), pedipalpi, and 4 pairs o"f legs ; but abdomen usu- 

 ally limbless. Breathe air by trachea, lung-books, or the skin. 



Order 1. Acarina, mites. Abdomen fused with rest of body ; respira- 

 tion by skin or trachea?. Demodex folliculorum, hair-sheath mite, 

 hermaphrodite. Sarcoptes scabiei, itch-mite, with suctorial cone and 

 pincer-shaped chelicera?. The females dig deep burrows in the epidermis, 

 in which they live ; hexapod larvse. Tyroglyphus siro, cheese-mite. 

 Ixodes ricinus, with trachea? and two stigmata. Hydrachna cruenta. 

 the six-legged larva? parasitic on aquatic insects. 



Order 2. Pycnogonida (Pantopoda). Marine forms of doubtful affinities, 

 with rudimentary abdomen, and four pairs of walking legs. Cutaneous 

 respiration. Pycnogonum littorale. 



Order 3. Tardigrada, water-bears. Minute aquatic hermaphrodites, 

 with piercing and sucking mouth parts, and four pairs of short walking legs. 

 Devoid of circulatory and respiratory organs. Macrobiotus Hufelandii. 



Order 4. Linguatulidce. Parasites without trachea 1 . Sexes separate. 

 Pentastomum tsenioides in the nasal cavities and frontal sinus of the 

 wolf and dog. The embryos pass on to herbage and with this into the 

 stomachs of the hare and rabbit, also of man, perforate the intestinal wall, 

 encyst themselves in the liver, and lastly reach the final host with the 

 flesh. 



Order 5. Araneida, spiders. With poison-glands in the subchelate 

 chelicera?, pedipalps ambulatory, abdomen unsegmented. Two or four 

 lung-books, six or four spinning papillae. Four lung-books : Mygale 

 avicularia. Cteniza csementaria makes tubes with trap doors in the 

 earth. Two lung-books : Salticus. Lycosa tarantula. Tegenaria 

 domestica, house spider. Epeira diadema, garden spider. 



Order 6. Phalangidce, harvestmen. With chelate chelicera?, slender legs, 

 and abdomen of six segments. Tracheate. Phalangium opilio. 



Order 7. Pedipalpi (Phrynidre). Clawed chelicer.-e, large pedipalpi, 

 slender first pair of legs, and two pairs of lung-books. Abdomen with 

 eleven to twelve segments. Phrynus. 



Order 8. Scorpionidce, scorpions. With chelate chelicera?, large chelate 

 pedipalpi, four pairs of lung-books, and poison claw at the end of the 

 tail. Abdomen with twelve segments and a telson ; abdominal append- 

 ages as genital operculum and pectines. Lateral and central eyes. Vivi- 

 parous. Scorpio Europseus. Androctonus. 



Order 9. Pseudoscorpionidce (Chernelida?). Small forms with large 

 chelate pedipalpi and a broad flattened abdomen of 10-11 segments. 

 Breathe by trachea?. Chelifer cancroides. Chernes. 



Order 10. Solifugce (Solpuga?). Head distinct from the thorax, which 

 has three segments ; abdomen with nine segments. Chelate chelicera? 

 and leg-like pedipalpi. Breathe by trachea?. Galeodes (Solpuga) 

 araneoides. 



