CHAPTER II 



JOINTED ANIMALS continued 



INSECTS continued 

 THE FLIES AND FLEAS Order DIPTERA 



As IMPLIED by their scientific name, the typical members of the order now 

 claiming attention are distinguished from all other insects by the possession of but 

 a single pair of wings. In this case one pair of these organs has disappeared, and 

 examination will reveal the fact that it is the front pair that is retained in full 

 functional importance, while the hinder pair has become reduced to a couple of short 

 slender club-like organs, known as halteres or balancers. From their small size it 

 might be supposed that these balancers were organs of but little physiological im- 

 portance, but the experiment of removing them will show that this is not the case; 

 for an insect thus mutilated is thereby entirely deprived of the power of maintaining 

 its equilibrium and of directing its course in the air. Hence the name balancers that 

 has been assigned to these rudimentary wings. The mouth parts, instead of being 

 of the primitive mandibulate type, are formed for purposes of piercing or sucking. 

 In the former kind of structure, as represented for instance in Pangonia longirostris, 

 one of the horseflies (Tabanidtz'), these organs are composed of seven pieces, which 

 have been interpreted by Mr. Waterhouse as follows: The uppermost is a long 

 pointed instrument, the labrutn. Immediately below this, and more or less con- 

 cealed by it, is an almost equally long and slender piece, which is probably the 

 hypopharynx. The mandibles are modified into a pair of sharp lancets, and below 

 them are two extremely slender instruments, which from the presence of palpi, are 

 recognizable as parts of the maxilla. All these pieces lie concealed in the basal half 

 of the proboscis, which, for part of its length, is gutter shaped, but afterward as- 

 sumes the form of a tube, and is believed to be comparable to the labium In the 

 gnats the mouth is formed upon the same plan, but the lancets are all more slender. 

 In piercing the skin the lancets only are used, the labium or proboscis serving 

 merely as a guide. In the flies that use the mouth for sucking as for instance in 

 the blowflies and drone flies the jaws are still more modified, so that the identity 

 of the separate pieces is difficult to establish. The most prominent part is the pro- 

 boscis, the expanding terminal lobes of which are the paraglossa of the labium. 

 The maxillae are represented by two scales or short stylets closely adherent to the 

 sides of the proboscis, and of two club-like palpi; but the mandibles seem to have 

 disappeared. 



The only characteristic that need be specially noticed in the wings is that they 

 are usually naked, being but rarely furnished with short hairs, and that the 

 veins are almost all longitudinal, that is, they run from the base or point of attachment 

 (3010) 



