II. 



DIPTERA. 



ALL suctorial insects which in the perfect state possess only two 

 membraneous wings, are called Diptera, from two Greek words 

 2/e, two, and ^repo*, wing. 



The Diptera were known and scientifically described at a very 

 early date. They are found often mentioned by Aristotle in his 

 History of Animals ; and he applied the term to the same insects 

 as now constitute the order. 



The absence of the second wings, common to other insects, 

 which are in this case replaced by two appendages, which have 

 received the name of balancers,* because they serve to regulate the 

 action of flight, constitutes the chief characteristic of the Diptera. 

 Let us, however, give a glance at their other organs, which have 

 more or less affinity with those which exist in other classes of 

 insects, preserving, nevertheless, their own especial characteristics. 



The mouth, for instance suited for suction only is in the 

 form of a trunk, and is composed of a sheath, a sucker, and two 

 palpi. The antennae are generally composed of only three joints. 

 The eyes usually two in number are very large, and sometimes 

 take up nearly the whole of the head. They are both simple and 

 compound. The wings are membraneous, delicate, and veined ; 

 the limbs long and slight. In giving the history of the principal 

 types of Diptera, we shall more fully explain the formation of 

 these organs. 



The Diptera, by their rapid flight, enliven both the earth and 

 the air. The different species abound in every climate, and in 



* Sometimes called halter es. ED. 



