42 INTERNAL ANATOMY OF INSECTS. 
some hawkmoths the intermediate ones are set in white 
or pale spots, which gives great life to the appearance 
of the animal. In general, in perfect insects the most 
prevalent colour is buff, or reddish-yellow. In the larva 
of the great water-beetle these organs resemble the iris of 
the eye, being circular with concentric rings alternately 
pale and dark 3 . 
4. The size of spiracles varies considerably. Those 
in the larva last mentioned are so minute as to be scarcely 
visible except under a lens, while those behind the fore- 
legs in the mole-cricket are a full line in length, and those 
in the pleura of Acrocinus accentifer, a Brazilian Capri- 
corn beetle, are more than twice as long. In the same 
species they are often found of different sizes; — thus the 
anal pairs in the water-beetle lately alluded to, I mean in 
the perfect insect, are much larger than the rest b , pro- 
bably that the animal may imbibe a larger quantity of 
air when it rises to the surface of the water, where it 
suspends itself by the tail. In those Lamellicorn bee- 
tles in which the terminal part of the abdomen is not 
protected by the elytra, the covered spiracles are the 
largest. 
5. Under the next head,, the situation of spiracles, I 
shall not only consider the part of the body in which 
they are situated, but likewise their position in the crust; 
to which last, as it will not detain us long, I shall first 
call your attention. Their position in this respect is 
most commonly oblique; but in the abdomen of the above 
water-beetle they are transverse, and in a larva I possess, 
probably of an Elater, they are longitudinal. In spinose 
' Sphinx Labrusae Merian Surinam. 3-J. 
» Plate XXIX. Fig. 28. A". 
