CLASS ARACHNIDA 23 



tion, are represented by fossils in early geological times, 

 and are noted as possessing poison glands. They are recog- 

 nized by the broad cephalothorax, a division of the abdomen 

 into two portions, an anterior preabdomen of seven seg- 

 ments, and a slender hinder postabdomen of six segments, 

 on the last one of which there is a large poison gland and 

 sting. The sting is distinctly venomous and fatal to insects 

 or smaller animals, but seldom serious in it's effect on the 

 human species. 



The Pseudoscorpionida are minute forms resembling 

 scorpions in the width of the body and the long pedipalps, 

 but have no postabdomen or sting. They occur somewhat 

 commonly under bark or decaying logs or occasionally in old 

 papers or books, where they may secure book lice as food. 



The Pedipalpi, or whip scorpions, have a tropical or 

 subtropical distribution and differ from the preceding groups 

 in the presence of a long, slender bristle or whip extending 

 from the hinder abdominal segment. 



In the group Solpugida there is an exceptional separation 

 of head and thorax and the abdomen is distinctly segmented, 

 while the chelicerai are greatly enlarged and strongly chelate. 

 These are not only largely tropical, but are particularly 

 characteristic of arid regions. One species occurs in the 

 Rocky Mountain region as far north as Colorado. They 

 are carnivorous in habit, but not of particular economic 

 importance, as they occur usually in small numbers and in 

 locations which do not offer opportunity to capture espe- 

 cially injurious insects. 



The Phalangida, or harvestmen, often called "daddy- 

 longlegs," are somewhat large and resemble spiders in 

 appearance, but the abdomen is not distinctly separated 

 from the thorax and the legs are in most species extremely 

 long. They feed on insects, especially on flies and other 

 small forms, and are to be counted as distinctly beneficial. 

 On account of a strong pungent odor they are disagreeable 

 to handle, but their presence in gardens and other places 

 where insects abound may be considered as distinctly desir- 

 able. 



