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SAIITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. IIO 



abdominal segment (fig. 14 B), and not the terminal segment itself. 

 The end segment, or telson, of an arthropod contains the anus; in 

 the scorpion the anus lies before the base of the sting in the end of 

 the sting-supporting segment (A, An). The scorpion sting in its 

 relation to the end of the abdomen is comparable with the flagellum 

 of the Thelyphonidae and the tail spine of Limulns. The base of the 

 sting is articulated on the end of the supporting segment in such a 

 manner that its principal movement is in a vertical plane, but because 



Fig. 14. — Tlie sting of a scorpion. 



A, Paiidiniis sp., end of last postabdominal segment, with the sting, ventral, 

 showing the anus (An) in last segment at base of sting. B, Ccntruroides sp., 

 last two postabdominal segments and the sting, lateral. C, same, the sting with 

 its muscles arising in the last segment. D, same, cross section through base of 

 sting, showing the venom glands and enclosing muscles. E, same, terminal part 

 of sting, showing aperture of left venom duct. F, same, right half of base of 

 sting, mesal view, showing muscles covering right gland, and duct. 



of the amplitude of the articular membrane it is capable also of 

 lateral movements. On its base are attached four long muscles, two 

 dorsal, and one on each side (C). The dorsal muscles are widely 

 divergent but both are inserted on a strong dorsal process of the 

 sting base. The lateral muscles are attached below the articular points 

 of the sting, and are hence depressors, but probably, acting as antag- 

 onists, they produce also lateral movements of the sting ; each lateral 

 muscle separates into two distinct bundles of fibers. The segments of 



