Marshall. — On New Zealand Diptcra. 225 



2. The Thorax. 



The mesothorax is very largely developed in this Order, 

 being so much larger than the prothorax and metathorax 

 that it forms the greater part of this division of the insect's 

 body. On account of this it is designated the thorax, different 

 names being given to characteristic parts of the prothorax 

 and metathorax. The former frequently forms a neck-like 

 prolongation that bears the head, and is then called the 

 neck icollum). In some cases the four corners of the meso- 

 thorax, or the shoulders [humeri), are covered by a lobe of the 

 prothorax {lohus protlioracis hmneralis) , distinctly separated 

 from the mesothorax. If this lobe be so soldered to the 

 mesothorax that it is impossible to detect a distinct line 

 between them, except in their general colour or luxir, it is 

 styled the shoulder callosity {callus kumeralis). When the 

 prothorax applies closely to the anterior border of the meso- 

 thorax it has then the name of collar (collare). An im- 

 portant character in its presence or absence is a transverse 

 furrow {suhira transversalis) frequently found crossing the 

 middle of the upper side of the mesothorax, and terminating 

 on each side just before the bass of the wing. On each side 

 of the breast, beneath the shoulder, there is a spiracle {stigma 

 protJioracis). The plate on the side of the breast is called the 

 pleura. The scutcheon {scutellwm) is separated from the back 

 of the mesothorax by a furrow^ and is situated between the 

 wings. , A part of the metathorax is to be found beneath the 

 scutellum ; it is called the metanotum. It generally descends 

 obliquely, is often convex, and has on each side a more- 

 or-less inflated space, called the lateral callosity of the 

 metanotum. The poisers, or halteres, have their origin be- 

 neath this callosity, and in front of each of them we find the 

 spiracle of the metathorax. The membranous covers some- 

 times found above this spiracle have the name of covering- 

 scales {squama or tegulce). 



3. Tlie Abdomen. 



The upper side is generally so called, the name of belly 

 {venter) being given to the lower side. The terminal joint is 

 furnished in the male with appendages destined to take hold 

 of the female in copula, and if they take hold in the form of 

 pincers and these are not bent under the body they are called 

 forceps ; in the female, with the organ for laying eggs {ovi- 

 piositor), which may be either called the bearer {tcnehra) or the 

 style {stylus), according to its shape. 



4. The Wings. 

 These organs need more close and special study than any 

 others in the distinction of species. The diagram (Plate VII., 

 15 



