140 ANATOMY AND PHYSIOLOGY 



or have been less carefully investigated, for a com- 

 paratively limited number of insects are mentionet 

 as possessing them. Among these are the carni- 

 vorous Coleoptera, Dytiscidse, Silphidee, certain Bra- 

 chelytrous species, a few Diptera, &c. Notwith- 

 standing their occasional complexity, we can for the 

 most part discern without difficulty an apparatus for 

 secretion, one or more deferential canals, and a re- 

 servatory bag emitting an excretory conduit which 

 empties itself into the rectum, just above the anus. 

 The fluids secreted are commonly colourless, and 

 highly caustic and odorous. These properties may 

 be easily determined by taking one of the larger 

 Carabi and handling it roughly, when it will probably 

 discharge the fluid, which it does with considerable 

 force in sudden jets, and if it fall on the skin, it pro- 

 duces a sharp burning sensation, which however is 

 very transient. In Carabus auratus the vessels in 

 question consist of two branches of globular bodies, 

 one on each side, resting on a footstalk, connected 

 with a long deferential canal, opening into a large 

 ovoid bladder. Chlcenius velutinus (PL II. fig. 7, a, a,) 

 has the secreting vesicles disposed on the tops of 

 small branchlets, so that the whole apparatus looks 

 not unlike a branch of a willow covered with catkins. 

 In the same fig. b is the deferential canal ; c, d, the 

 bladder. Fig. 8 in the same plate, represents these 

 parts as they appear in the Bombardiers, a kind of 

 beetles vhich have been long famous for possessing 

 the power cf producing an explosion accompanied 

 with a discharge of smoke. This is caused by the 



