ARTHROPODA. 



97 



Demodicid<e. Dermaiiyssus. 

 Demodex = Simonea. Pteroptus. 



SarcoptidcB. 

 Sarcoptes. 



Dermalichus=Anal- 

 ges=Myocoptes. 



Acaridte. 

 Acarus = Tyrogly- 



phus.' 



Glyciphagus. 

 Mjobia. 



GamasidcB. 

 G-amasus. 



Ixodida. 

 Argas. 

 Ixodes. 

 Amblyomrna. 



TrombidiidcB. 

 Tetranychus. 

 Leptus. 

 Linopodes. 

 Erythraeus. 

 Trombidium. 

 Pliytoptus. 



Hydrachn idee. 

 Limnochares. 

 Hydrachna. 

 Hydrochoreutes. 

 Atax. 



Oribatidce. 

 Halacarus. 

 Oribates = Notaspis. 

 IVothrus. 

 Hoplophora. 

 Damseus. 



Bdellidce. 

 Bdella. 

 Scirus. 



Pcecilophysis. 



Order IV. ARANEIDEA. (Spiders.) 



DlMEROSOMATA. PuLMOTRACHEAKIA. 



Respiration by pulmonary sacs, often combined with trachea;. 

 Abdomen distinctly separated from the cephalothorax, not seg- 

 mented. Two paipi. Eyes simple, 4-8. Eight feet, each of 

 seven joints. 



There are special abdominal glands for the secretion of a 

 gumrny fluid, which, exposed to the air, hardens into silk, used 

 for the construction of webs; they communicate externally with 

 the spinnerets by long convoluted vessels. There are also special 

 glands for the secretion of a poison, placed at the base of the 

 falces or poison -fangs ; these are situated between the eyes and 

 the mouth, and are hollow for the passage of the fluid. The 

 mouth has two maxillte, each of which bears a palpus, often leg- 

 shaped. In the male spiders the parts analogous to the vesiculse 

 seininales ai*e lodged in these maxillary palpi, but the testes are, 

 as usual, in the abdomen. The males are much smaller and weaker 

 than the female, and are frequently sacrificed to her savage in- 

 stincts etiam in amoribus scst-a. They moult when growing, but 

 there is no metamorphosis. In the embryonic state there is a 

 postabdomen which gradually disappears. Arthrolycosa, a fossil 



