414 ORDERS OF PTILOTA. 



the bee be compared together with the wing of some flies, 

 as the Syrphidce, and particularly Aphrites, we are enabled 

 to trace a very great resemblance between them in this re- 

 spect. M. Macquart employs this circumstance as a forcible 

 argument in support of the opinion that the balancers of the 

 Diptera do not rejn-esent the lower wings of the bee. The 

 uses to which these balancers are applied are not yet de- 

 cidedly ascertained : the insect moves them with extreme 

 rapidity, especially when a buzzing noise is produced ; and 

 it is important to observe that they are placed close to the 

 mouth of a pair of the breathing pores. Many species are 

 moreover provided at the base of the wings behind with a 

 pair of membranous doubled organs, somewhat like the valves 

 of a shell, which are termed alulets: one of these is attached 

 to the wing, and the other to the sides of the thorax. The 

 size of these alulets is in inverse proportion to that of the 

 halteres. The abdomen is generally attached to the thorax 

 by a portion only of its basal diameter : it is composed of 

 from five to nine visible articulations, and is generally pointed 

 at the extremity in the females, enabling them the more 

 readily to introduce their eggs into the situations in which 

 they are deposited. In those species which have the abdo- 

 men composed of the fewest segments, those which appear 

 to be wanting are transformed into a kind of ovipositor, con- 

 sisting of a series of little tubes, sliding one into another 

 like a telescope. The sexual organs of the males are ex- 

 ternal in many species, and folded beneath the abdomen. 

 The legs are terminated by a tarsus consisting of five joints, 

 the last of which is armed with two small claws, and very 

 often with two or three membranous lobes or pulvilli. It is 

 by the assistance of these terminal organs of the foot that 

 the fly is enabled to perform the cm-ious mechanical feat of 

 walking with the back downwards, against gravity, upon the 

 ceilings of rooms, highly polished glass, &c. From the ex- 



