26 CHARACTERS OF THE DIPTERA. 



rudimentary wings, but are wings which have become sub- 

 servient to a new function, and have undergone a corresponding 

 modification of structure. The mouth organs in the Diptera 

 are also so different from those of other insects that they have 

 been the subject of much controversy, and their morphology 

 has never been satisfactorily settled ; the parts of the mouth 

 are exceedingly complex, and differ far more profoundly from 

 the primitive type than either the tongue of the bee or the 

 spiral antlia of the Lepidoptera. 



Haeckel regarded the Coleoptera, or beetles ; the Hymen- 

 optera, or bees and wasps ; the Lepidoptera, butterflies and 

 moths ; and the Diptera, or two-winged flies, as the extreme 

 modification of four separate and divergent genetic series, 

 just as mammals, birds, and reptiles are amongst the verte- 

 brates. The Coleoptera have apparently descended from 

 Orthoptera : the Hymenoptera and Lepidoptera from Neu- 

 roptera ; and the Diptera from Hemiptera : or rather from 

 ancestral forms similar to those which form these less 

 specialised orders. Just as all discussion would be futile as to 

 whether a bird or a mammal is the higher type, so it is useless 

 to consider whether the Diptera or the Hymenoptera have the 

 higher organisation ; but there can be no question as to which 

 of these orders departs most from the more generalised form. 

 The Diptera are far more remarkable in their developmental 

 history, and in the modification of structure which they present 

 in the adult or imago form. In this relation the strong ten- 

 dency of many to produce their young alive, and the fact that 

 some have a capacious matrix, or uterus, in which the larvae 

 are hatched, or even attain the pupa form, before birth, is not 

 without interest presenting as it does some analogy with the 

 viviparous character of the Mammalia amongst vertebrates 

 whilst the nest-building instincts are more manifest in 

 Hymenoptera and in birds. It is true that the flies, and more 

 especially the heavy forms, with a comparatively tardy flight, 

 like the blow-fly, have been regarded as 'stupid' Sprengel called 

 them ' die dumme Fliegen ' and do not excite our sympathy 

 and curiosity to the same extent as the social Hymenoptera ; but 



