354 Lmnean Society. [Dec. 7? 1847. 



formed beneath the old skin of the larva some days before its change. 

 These folds of tegument supplied each with their tracheae closely re- 

 semble in appearance the external abdominal branchiae of the aqua- 

 tic larvse oi Neuroptera," and afterwards become the most important 

 organs of the insect in its perfect state — the wings. The expansion 

 of these organs at the change is mainly effected by their tracheae, 

 which instead of becoming dilated, like those within the body, are 

 elongated, and thus induce a rush of blood into these portions of the 

 tegument which promotes their expansion into wings. This elon- 

 gation, as well as the dilatation of the tracheae within the body, is 

 the result of powerful respiratory efforts of the insect. The author 

 remarked, that although able to show the mode in which these 

 changes are effected, it is less easy to give a satisfactory explanation of 

 the real use of the vesicles. He adopts, however, a view entertained 

 by John Hunter, that the vesicles are mainly to enable the insect to 

 alter the specific gravity of its body at pleasure during flight, and 

 thus diminish the muscular exertion required during these move- 

 ments. To support this opinion, the author reviewed the different 

 classes of Vertebrata, and showed that although a vesicular form of 

 the respiratory organs exists in the whole, yet that Birds approach 

 much more closely to Insects in this respect, as well as in the more 

 extensive distribution of the organs themselves, than any other of 

 the Vertebrata ; and he referred to the fact that in apterous insects, 

 as in birds that are unaccustomed to flight, the respiratory organs 

 are less capacious or less extensively distributed. This fact, he 

 stated, is not confined to insects of which both sexes are apterous, 

 but that when one sex is winged and active in flight, and the other 

 apterous, he has always found the body of the former with vesicular 

 tracheae, while in the other, the apterous sex, the tracheae are sim- 

 ply arborescent, as he has found in the sexes of the glow-worm, and 

 in the common winter-moth, Geometra trumaria. These facts, in- 

 ferential with regard to the use of the vesicles, the author supported 

 with an account of an experimental observation on the mode in which 

 the common dung-beetle prepares itself for flight, by rapidly in- 

 creasing its respiration and distending its body the instant before 

 it unfolds its wings and attempts to raise itself upon them. 



