STING STRUCTURE. 185 



first to enter when the sting is used. The puncture 

 having been made, the sheath is held in the wound 

 by two* rows, each containing three, or unusually 

 six, microscopic teeth (E, Plate VII.), pointing back- 

 wards, and acting like the barbs of an arrow or 

 harpoon. The sheath has three functions : first, to 

 open the wound as we have seen ; secondly, to act 

 as an intermediate conduit for the venom ; and, 

 thirdly, to hold in accurate position the long darts ter- 

 minated by barbs (5, A, Plate VI., and E, Plate VII.). 

 The sheath, so-called, does not inclose the darts 

 as a scabbard, but is cleft down the side presented 

 to us in Plate VI., which is below when the sting 

 points backwards. This cleft at the upper part 

 of the sheath, where the latter is oval in cross 

 section, is just wide enough to permit the two darts 

 to close it by standing side by side between its 

 edges. But as the darts move up and down at their 

 pain-inflicting work, they would immediately slip 

 from their position, unless prevented by a mechanical 

 device, exhibited by B and C, Plate VI., giving 

 in cross section sheath and darts near the termina- 

 tion, and at the middle of the former. The darts 

 (d) are each grooved through their entire length, 

 while upon the sheath (sh) are fixed two guide rails, 

 each like a prolonged dovetail, which, fitted into the 

 groove, permits of no other movement than that 

 directly up and down, to which we have previously 

 referred. At E, Plate VII., the dart has been 



* Mr. Hyatt, who has carefully examined the sting {American 

 Quarterly Microscopical Journal, vol. i.), has found only one row, but 

 two always exist, although they are difficult to bring into view. 



