178 SYSTEMATIC ZOOLOGY 



then suck the fluids from the body. The cephalothorax is rela- 

 tively short and bears the typical six pairs of appendages, the 

 first pair very small, the second the largest of all, the others 

 simple walking legs. On the dorsal side of the cephalothorax 

 are from two to six pairs of eyes ; usually one pair is large and 

 situated near the median line, the others being more lateral in 

 position. 



The abdomen is very long, distinctly segmented, and divided 

 into two parts, the large, rounded preabdomen consisting of 

 seven segments, and the more slender postabdomen consisting 

 of six segments ; this latter portion is commonly called the tail. 

 On the ventral side of the first abdominal segment is the genital 

 opening, provided in the male with a double penis. Just pos- 

 terior to the genital opening is a pair of comblike appendages, 

 the pectines, probably sensory in function. Then in each of the 

 four succeeding segments, the third, fourth, fifth, and sixth, is a 

 pair of slitlike stigmata, which connect with the four pairs of 

 lung books or respiratory chambers. 



The segments of the postabdomen are all very much alike 

 except the last. This is provided with a sharp spine at whose 

 tip is the opening of a pair of poison glands situated within. 

 The anus is at the base of the last segment, just at the posterior 

 end of the fifth, so that the postabdomen may be regarded as 

 consisting of five segments, with the poison glands contained 

 in an appendage of the fifth segment (Fig. 172). When walking, 

 the postabdomen is carried curved upward over the dorsal side 

 of the body and then is suddenly lowered when the animal 

 washes to strike anything. The poison kills small animals 

 instantly ; the sting of the largest species may possibly be fatal 

 to man, at any rate it produces a very unpleasant illness. The 

 scorpions are viviparous, the young being born in a condition 

 differing but little from the adult except in size. 



Order 2. Pseudoscorpionida 



The Pseudoscorpionida (Gr. ijrev&rjs, false, and afcopTri'os, scor- 

 pion) are minute Arachnida, often less than two millimeters in 

 length, which live under the bark of trees and in old books, and 

 hence are sometimes called book scorpions (Fig. 173). The 



