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 a . 



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 



a Sphinx Labruscce Merian Surinam, 34. 

 PLATE XXIX, FIG, 28. A'. 



