28 



DIPTERA OF MINNESCTA. 



inner or air tube enclosed in an outer tube, which latter carries 

 blood at an early stage of its formation. 



The venation or neuration of a fly's wing, that is, the ar- 

 rangement of the veins, is so important that we have ventured to 

 include under the various families a number of illustrations, show- 

 ing dififerent types. A student working with Diptera soon be- 

 comes so familiar with the venation in the dififerent families that 

 he can tell at a glance the group to which his specimen belongs. 

 These figures have been taken from Comstock, and in reproduc- 

 ing his excellent drawings we reproduce his method of numbering, 

 which, it must be said, is not now generally used. The cells of the 

 wing, that is, the spaces enclosed by the nerves, are named in each 



Vig. 9. Different types of antennae found amongst the flies. A, the two antennae of a 

 Mycetophilid; B, antenna of the Tabanidae; C, Asilidae; D, Leptidae; E, Dolicho- 

 podidae; F, Syrphidae; G, Chironomidae (male); H, Muscidae, H and 1- are 

 similar. Figs. A, B, C, D, E, and F after Wandolleck; G and H after Comstock, 

 much enlarged. 



case from the vein just in front of that cell. For example, in the 

 illustrations, the cell just behind Vein III, is cell III; the cell 

 behind II is cell II, and so on. Where a vein represents the coal- 

 escence of two, like III 2+3 the cell behind is cell III3, taking its 

 name from the last numbered vein. When a cell is completely sur- 

 rounded by cells it is said to be closed, but when it extends to edge 

 of wing it is open. The base of the wing is where it is attached to 

 the thorax; the apex is the opposite end. 



The abdomen, consisting of several rings or segments, making 

 up the posterior part of the fly's body, is well shown in Fig. 4. 

 On the side of each segment of the abdomen shown in the drawing 

 is a small hole, a spiracle, through which the air is drawn in respi- 

 ration, being distributed by means of small tubes called tracheae 



