INSECTA. 263 



saliva. These glands are principally met with in suctorial insects, 

 but not unfrequently among the mandibulate orders. Their form 

 varies ; but they are generally simple slender tubes, that float 

 loosely among the juices of the body, from which they separate the 

 salivary fluid. There are, for the most part, only two of these 

 organs (fig. 117, s, s) ; but in fleas (Pulex), and bugs (Cimex), 

 there are four, and in a water-bug (Nepa), there are six such 

 vessels, all of which open into the cavity of the mouth. The 

 fluid supplied by the salivary glands is usually merely intended to 

 facilitate deglutition ; but there are cases in which the saliva is ex- 

 cessively acrid and irritating, acting as a kind of poison when in- 

 fused into a puncture made by the mouth : this is especially re- 

 markable in many bugs and gnats, and is the chief cause of the 

 pain and inflammation frequently occasioned by their bite. 



Besides the proper salivary vessels, there are other glands, or 

 rather caeca, which open into the stomach itself, occasionally cover- 

 ing that organ over its entire surface, as is the case in some water- 

 beetles (Hydrophilus) ; these, no doubt, secrete a fluid subser- 

 vient to digestion ; but whether of a peculiar description, or allied 

 to saliva in its properties, is unknown. 



The third kind of auxiliary vessels connected with the intestinal 

 canal of insects, is supposed to furnish a secretion analogous to 

 the bile of other animals, and consequently to represent the liver. 

 The bile-vessels (fig. 116, A, h; fig. 117,#, g) are generally four, 

 six, or eight in number, but occasionally much more numerous ; 

 they are usually of great length, but exceedingly slender, and wind 

 around the intestine in all directions. When unravelled, they are 

 found to terminate, in the neighbourhood of the pylorus (fig. \ 17, 

 A, w), close to the commencement of the intestine, at which point 

 the secretion produced by them is mixed with the food after it has 

 undergone the process of digestion. 



Appended to the termination of the alimentary tube, close to 

 its anal extremity, other vessels are met with in some insects that 

 are looked upon by authors as being allied in function to the kid- 

 neys of higher animals ; but apparently this opinion rests upon 

 very doubtful grounds. They indubitably furnish some secretion, 

 the use of which is perhaps connected with defecation ; but that it 

 is of the same character as the fluid separated by the renal organs 

 of vertebrata may well be called in question, as no such parts are 

 distinctly recognisable until we arrive at much more elevated forms 

 of life than the insects we are now considering. There is, how- 



