XI 



PHYLUM ARTHROPODA 



657 



The organs of respiration in the Scorpions are in the form of 

 pulmonary sacs or book-lungs (pul.), the stigmata or external openings 

 of which have already been referred to. Each pulmonary sac is 



a compressed chamber lined with a thin cuticle. The lining 

 membrane is raised up into numerous delicate laminae lying 

 parallel with one another like the leaves of a book. Into the 

 numerous narrow spaces between the lamina; the air penetrates, 



