55^ PHILOSOPHY OF ZOOLOGY. 



2d Tribe. 



Lungs tracheal. Eyes two or lour. 



A. Thorax and abdomen distinct. Eight feet. There 

 are three genera. Solpuga, Chehfer, and Obisium. 



B. Thorax and abdomen united. 



1. Mandibles distinct , of two or three pieces, tlie last of 

 which IS cheliferous. 



a. Mandibles prominent. Phalangium and Sirio. 

 h. Mandibles not prominent. Trogulus. 



2. Mandibles either in one piece, or in the form of an 

 hausteUum. 



a. Legs eight. 



(L) Legs formed for walking. 



(a.) With a haustellum, with or without palpi. Ixo- 

 des, Argas *, Uropoda, Smaridia, and Bdella. 



(bb.) Mandibles distinct, and palpigerous. 



(a.) Palpi with simple extremities. Mandibles chelife- 

 rous. Acarus, Cheyletus, Gamasus, and Oribata. 



(6.) Palpi subcheliferous. Mandibles with a claw. 

 Erythraeus and Trombidium. 



(2.) Legs fringed, and formed for swimming. Hy- 

 drachna, Elais, and Limnochares. 



h. Legs six. Caris, Leptus, Atoraa, and Ocypete. 



Section IL 

 Head furnished with antenna, and compound eyes. 

 This section includes the groups termed Insecta and 

 Myriapoda. 



I.— INSECTA. Insects. 

 Feet six, supported by the thorax. 



The arrangement of insects has occupied the attention 

 of many acute and accomplished naturalists. As yet, how- 



* a species nearly related to this genus, found on Falco tinnunculus, is 

 given in Plate IV, f. 7. 



