FIELD BOOKTOF INSECTS. 



I do not expect that this brief discussion will satisfy the 

 reader who attempts to apply it to all Diptera ; such special 

 students should go to special books such as Williston's 

 Manual of North American Diptera. 



Some Diptera have thread-like or feathery antennas 

 with numerous similar joints; others, such as the ordinary 

 house-flies, have stubby antennae with only three joints, 

 the third bearing an arista. This .arista may be bristle- 

 like and either feathered or plain; placed dorsally or at 

 the tip of the third joint. If it is at the tip and is rela- 

 tively stout, it is called a style. The forms of antennae 

 are numerous and varied. The space between the eyes 

 and above the roots of the antennas is called the front. 

 The vertex is the top of the head between the eyes. 



The various parts of the thorax have been named and 

 are often important taxonomically. Plate LXIX shows 

 the aclirostical (a.) and dorsocentral (d. c.) series of bristles 

 divided by the transverse suture (t. s.). The letter a. is 

 placed on the scutellum. 



The following key divides ordinary flies into two sub- 

 orders: Nematocera and Brachycera. Another way of 

 dividing the order is as follows: those flies whose larvae 

 have a differentiated head, and whose adults leave the 

 surrounding pupal covering through a T-shaped opening 

 on the back of the anterior end, or rarely in a transverse 

 rent between the eighth and ninth abdominal rings, belong 

 to the suborder ORTHORRHAPHA; those flies whose 

 larvae do not have a differentiated head, whose pupae are 

 enclosed in the hardened larval skin (forming the so-called 

 puparium), and whose adults leave from the anterior 

 end through a circular orifice (the adults have an oval or 

 crescentic space, the "frontal lunule," above the roots of 

 the antennae, and usually have a "ptilinum," an inflatable 

 organ capable of being thrust out just above the roots of 

 the antennae which is used by the adult in springing off the 

 cap of the puparium), belong to the suborder CYCLOR- 

 RHAPHA. All Nematocera are Orthorrhapha and so 

 also are all Stratiomyidae, Tabanidae, Leptidae, Asilidae, 

 Bombyliidae, Dolichopodidae, and their near relatives 

 among the Brachycera. 



230 



