THE ALIMENTARY CANAL. 



13 



bombardier beetle, Brachinus, with its anal glands, ejects a jet of: 

 bluish vapour accompanied with a considerable explosion, which 

 colours the human skin rust-red; it is caustic, smells like nitrous 

 acid, and turns blue paper red. Westwood states that individuals 

 of a large South American Brachinus, on being seized immediately 

 began to play off their artillery, burning and staining the flesh to 

 such a degree that only a few specimens could be captured with the 

 naked hand, leaving a mark which remained for a considerable 

 time. The fluid ejected by another species, in Tripoli, blackened 

 the Angers of the collector. It is neither alkaline nor acid, and it 

 is soluble in water and in alcohol " (Kirby and Spence, iv, p. 149). 



" Species of other genera (Agonum, PJieropsoplms, Gdlerita, 

 Paussus, Ozcena) are also bombardiers [the power is especially 

 noticeable in Pheropsophus], A Paussid beetle {Cerapterus) ejects 

 explosively a fluid containing free iodine (Loman), while Staphy- 

 linus, Stenus, Ocypus, Lacon, etc., have similar anal foetid glands, 

 the liquid being more or less corrosive. The secretion of Mormolyce 

 phyllodes is so corrosive that it is said to paralyse the Angers for 

 21 hours after" (Cuenot, quoted by Packard). 



The larva of Hydrophilus piceus ejects a black fcetid fluid from 

 the anus ; the Dytiscid.e eject a colourless disagreeable fluid ; the 

 SiLPHiDiE have only one anal gland from which they throw out an 

 ammoniacal liquid. There are, of course, mauy other secretions 

 emitted by Coleoptera, but these do not arise from the anal glands 

 and are best considered under the separate families. 



We have already alluded to the Malpighian tubes. These are 

 attached to the junction of the stomach and intestine, and are 

 present in almost all insects, but vary very greatly in leugth, shape, 

 and number, sometimes only two being present and sometimes a 

 hundred or more; they derived their name from the Italian 

 anatomist Malpighi who first discovered them. At first they were 

 thought to be biliary tubes, but were afterwards regarded as ex- 

 cretory or urinary organs, answering to the kidneys of the higher 

 animals. In the Coleoptera their number is either four or six, 

 and this difference, which will be again alluded to, has been repre- 

 sented by authors as an important point in the classification of 

 the order. 



The salivary glands and the silk glands are offshoots of the 

 oesophagus, the former being present in many insects, but absent 

 in others, and varying very much in size. They consist " either 

 of simple tubes lined with cells or of branched tubes, or of 

 tubes dilated laterally into little acini or groups of bags, the 

 arrangement then somewhat resembling that of a bunch of grapes. 

 There are sometimes large sacs or reservoirs connected with the 

 efferent tubes proceeding from the secreting portions of the glands. 

 The salivary glands ultimately discharge into the mouth, so that 

 the fluid secreted by them has to be swallowed in the same manner 

 as the food, not improbably along with it" (Sharp). In Anoph- 

 thalmus there are three pairs of salivary glands, while in Blaps 



