ORDER XVI. DIPTERA. 



This order is by far the most interesting if we con- 

 sider structural characteristics and development. The 

 reasons for assigning the group its position as repre- 

 sentative of extreme specialization are suggested in 

 the descriptive work on the type and succeeding fam- 

 ilies, and stated in comprehensive form in the con- 

 cluding remarks (see pp. 273, 274, 287). We regret 

 that space will not permit us to give detailed descrip- 

 tions and figures of the many interesting modifications 

 of structure which characterize pre-eminently both 

 the larval and adult stages of this large order. 



As a rule the Diptera are small insects, and there- 

 fore good specimens for close observational work. 

 Scholars should become acquainted with their struct- 

 ure and transformations, and this can be done if it is 

 remembered that after continued observation the eyes 

 distinguish characteristics which are not at first visible, 

 and that magnifiers of cheap construction will do a 

 surprising amount of work in the hands of any one 

 with sufficient perseverance. 



The familiar house-fly, Mitsca domestica, Linn., can 

 be used as the type, if other species are not at hand. 

 The horse-fly, or '' green-head," Tabaniis lineola, 

 Fabr. (PI. XII., Fig. 196, p. 248), is larger, and its 

 mouth parts are more perfectly developed, so that it 

 can furnish good examples for class instruction. 

 .48 



