300 ENTOMOLOGY FOR MEDICAL OFFICERS 



The OpisthothelcB are divided into two suborders, namely, 

 (i) Mygalomorpha, in which the chelicerse are directed for- 

 wards and their fang closes backwards, and the lung-sacks 

 are two pairs ; and (2) the Arachnomorpha, in which the 

 chelicerae are directed downwards and the fang closes 

 obliquely inwards, the pedipalps always have a maxillary 

 process, and the breathing-organs consist of one pair of lung- 

 sacks and a pair of tracheae. 



The Mygalomorpha for the most part live in burrows 

 which are generally lined with silk. Some of them, known 

 as Trapdoor-spiders, stop the mouth of the burrow with a 

 hinged and very accurately fitted lid which opens outwards. 

 Some of the tropical Mygalomorpha are of very large size, 

 and are said to prey upon small birds and small mammals. 



Fio. 132.— iafArodcciM. 



The Arachnomorpha, which include an enormous number 

 of species, are the ordinary familiar spiders. Some of them 

 wander about and run their prey down or leap upon it, 

 others make webs which may either be irregular in form or 

 be beautifully woven of concentric threads on radial stays. 



Order SOLIFUG^ 



Spider-like Arthropods differing from all other Arachnida 

 in having the segments of the body grouped in three regions 

 — head, thorax, and abdomen — like an insect. The head 

 carries the chelicerae, the pedipalps, and — in the middle of 

 the front border— a pair of eyes. Each chelicera consists of 

 a swollen basal piece and two fangs, which work like pincers ; 



