232 Dv Davy on the Excrements of certain Insects. 



under glass. A good deal of water was exhaled and condensed 

 in the upper part of the vessel ; and some excrement, about the 

 third day, was voided on the side of the glass — semifluid, and 

 of a greyish hue. Tested by nitric acid, it was found to con- 

 tain lithic acid. The old wasps, at this time, were feeding on 

 the comb. A young wasp, nearly full grown, was taken from 

 its cell for examination. The lower portion of its intestine 

 was found distended with a soft white matter, consisting al- 

 most entirely of lithic acid in minute granules ; — such was its 

 appearance under the microscope ; and, heated with nitric 

 acid, the colour was produced characteristic of lithic acid. 



Cockroach. — In laying open the abdomen of one of these in- 

 sects, a whitish matter soiled the knife, which appeared to 

 come from a tubular apparatus on each side of the intestine, 

 performing, no doubt, the function of the kidney. The matter 

 was abundant, and, by the test of nitric acid, it was proved to 

 be chiefly lithic acid. 



Moth. — A brown moth, with a body about half an inch long, 

 died, after having been confined under glass a few hours. A 

 very minute portion of brown semitransparent excrement was 

 obtained, found deposited on the bottom of the vessel, which, 

 acted on by nitric acid and heat, was ascertained to be chiefly 

 lithic acid. 



That the urinary secretion of the five difi'erent insects 

 named was principally lithic acid, either pure or combined 

 with ammonia, I apprehend cannot be questioned ; the results 

 were so distinct and satisfactory. This is not uninteresting 

 physiologically, — shewing how little aggregate-form, and how 

 little the kind of diet is concerned in the nature of the secre- 

 tion. There is another point of view, in which also it is not 

 uninteresting. Hitherto the insect tribe has been considered 

 chiefly destructive of vegetation, whether in the form of grub 

 or caterpillar, or mature state : they have not had credit for 

 any compensating power — for contributing to the fertility of 

 one plant, whilst feeding upon, and, perhaps, destroying another. 

 And yet this conclusion seems unavoidable in the instance of 

 those insects, the urinary secretion of which is chiefly lithic 

 acid. From analogy it may be inferred that such is the ex- 

 crement of the locust ; and if so, the vast flights of this insect, 



