LEPIDOPTEROUS INSECTS. 79 
Although insects appear to have dry, rigid mouths, 
yet they possess the salivary glands, which are ne- 
cessary for moistening their food, and fitting it for 
mastication. Professor Rennie has recently made 
some conclusive experiments on this interesting sub- 
ject. He says, “ one of the circumstances that first 
awakened our curiosity with regard to insects, was 
the manner in which a fly contrives to suck up, 
through its narrow sucker, (or hawstellum,) a bit of 
dry lump sugar ; for the small erystals are not only 
unfitted to pass, from their angularity, but adhere 
too firmly together to be separated by any force the 
insect can exert. Eager to solve the difficulty—for 
there could be no doubt of the fly’s sucking the dry 
sugar—we watched its proceedings with no little 
attention ; but it was not till we fell upon the de- 
vice of placing some sugar on the outside of a win- 
dow, while we looked through a magnifying glass 
on the inside, that we had the satisfaction of re- 
peatedly witnessing a fly let fall a drop of fluid upon 
the sugar, in order to melt it, and thereby render it 
fit to be sucked up,—on precisely the same principle 
that we moisten with saliva, in the process of mas- 
tication, a mouthful of dry bread, to fit it for being 
swallowed,—the action of the jaws, by a beautiful 
contrivance of Providence, pressing the moisture 
along the channels at the time it is most wanted.” 
To the investigations of Swammerdam, we are 
indebted for our first knowledge of these vessels. 
