444 INVEHTMBHATE MORPHOLOGY. 



tlie pages of books, and lience being known popularly as the 

 Book-scorpion. The cephalothorax is unsegmented, and is 

 followed by a broad flattened abdomen composed of eleven 

 segments. A prseabdomen and a postabdomen, such as can 

 be distinguished in the Scorpionida, does not occur, nor is 

 there a terminal poison-spine nor a poison-gland. 



The chelicerse and pedipalps resemble those of the Scor- 

 pions, being chelate, and the four succeeding appendages are 

 walking-legs, while the abdomen pos- 

 sesses no appendages in the adult. Both 

 the second and third abdominal seg- 

 ments bear upon their ventral surfaces a 

 pair of stigmata which are the openings 

 of tubular tracheae which extend through 

 the body sending off branches, except 

 in Chernes, in which bunches of un- 

 branched tracheae arise from each stig- 

 ma. A heart is present, but consists of 

 Fig. ^O'i.^Ghelifer card- a simple tube with either a single pair 

 nmdes (from uuvieb). ^f ostia near its posterior extremity 

 {Obisium) or with four ostia {Chernes). 

 The endodermal portion of the digestive tract gives rise 

 to a pair of lateral csecal diverticula branched at the apex and 

 to one unpaired ventral one. Two eyes are present in Chdifer 

 and four in Ohisium, while they are entirely wanting in 

 Chernes. The reproductive organs open upon the ventral sur- 

 face of the second abdominal segment, and the opening is 

 surrounded with glands which secreie a fluid which quickly 

 hardens to silky filaments and serves to fasten the eggs to 

 the abdomen of the parent. These glands are hypodermal in 

 origin and correspond to the spinning-glands of the Spiders. 



3. Order Solifugse. 



The members of this order are characterized by the head- 

 region being separated from a thorax consisting of three seg- 

 ments and bearing the three posterior pairs of legs. The 

 abdomen is also segmented, its ten segments showing no dif- 

 ferentiation into praeabdomen and postabdomen, nor does it 



