458 INVERTEBRATE MORPHOLOGY. 



Pedipalpi are more primitive as regards the number of abdominal seg- 

 ments and their distinctness than the Araneas, yet the latter and especially 

 the Tetrapneumones show a much more primitive condition of the respira- 

 tory organs. With regard to these organs it may be stated that the con- 

 dition in which they are represented by bunches of uubrauched tracheae 

 is more primitive than that in which they are branching tubes, the 

 bunched condition being probably derived by a modification of original 

 lung-books. 



TYPE ARACHNIDA. 



1 . Order Scorpionida. Abdomen segmented and differentiated into prae- 



abdomen and postabdomen ; postabdomen terminating in poison- 

 spine ; pedipalps chelate ; two pairs of abdominal appendages ; 

 four of stigmata and lung-books. Euscorpius, nth us. 



2. Order Pseudoscorpionida. Abdomen segmented but not differentiated ; 



no terminal spine ; pedipalps chelate ; no abdominal appen- 

 dages ; two pairs of stigmata opening into tracheae ; first pair 

 of legs adapted for locomotion. Chelifer, Obisium, Chernes. 



3. Order Solifiigce. Head separated from thorax with three segments ; 



abdomen segmented but undifferentiated ; no terminal spine ; 

 pedipalps palplike ; three pairs of stigmata leading into tracheae. 

 Galeodes, Solpuga. 



4. Order Pedipalpi. No distinction of head and thorax ; abdomen seg- 



mented, and either undifferentiated or with three small segments 

 terminated by a multiarticulate flagellum ; pedipalps leglike or 

 subchelate ; two pairs of stigmata and lung-books ; first pair of 

 legs elongated and palplike. Phrynus, Thelyphonns. 



5. Order Phalangida. Abdomen segmented but undifferentiated and 



without appendages or terminal spine ; pedipalps leglike ; one 

 pair of stigmata leading into tracheae ; no spinning-glands. 

 Leiobii'iium, Phalangium, Opilio, Gonyleptus, Cyphophthalmus, 

 Gibbocellam. 



6. Order Araneoe. Abdomen unsegmented and with two or three pairs of 



rudimentary papillalike appendages bearing the openings of 

 ducts of numerous spinning-glands ; abdomen not fused with 

 cephalothorax ; pedipalps long and palplike or leglike. 



1. Suborder Tetrapneumones. With four stigmata opening into 



sacs containing lung-books. Mygale, Cteniza. 



2. Suborder Dipneumones. With four or three stigmata, the anterior 



pair opening into sacs with lung-books, the posterior one or 

 two with tracheae. Epeira, Agelena, Tegenaria, Theridium, 

 Seyestria, Attus, Lycosa. 



7. Order Acarina. Abdomen unsegmented, without appendages, and 



fused with the cephalothorax ; pedipalps sometimes long and 

 leglike, sometimes chelate ; stigmata wanting or present as a 



