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THE ORDERS OF FLIES. 187 
of Gauze-winged Flies (Neuroptera), probably developed 
directly out of the primeval Flies, which differ from them 
only by their perfect series of transformations. Among them 
are the gauze-flies (Planipennia), caddis-flies (Phryganida), 
and fan-flies (Strepsiptera). Fossil Flies, which form 
the transition from the primeval Flies (Libellula) to 
the gauze-winged (Sialidz), are found even in coal 
(Dictyophylebia). 
The order of Straight-winged Flies (Orthoptera) de- 
veloped at an early period out of another branch of the 
primeval Flies by differentiation of the two pairs of 
wings. This division is composed of one group with a 
great variety of forms—cockroaches, grasshoppers, crickets, 
ete. (Ulonata)—and of a smaller group consisting only of 
the well-known earwigs (Labidura), which are character- 
ised by nippers at the hinder end of their bodies. Fossil 
remains of cockroaches, as well as of crickets and grass- 
hoppers, have been found in coal. 
Fossil remains of the fourth order of Biting Fhes, 
beetles (Coleoptera) likewise occur in coal. This extremely 
comprehensive order—the favourite one of amateurs and 
collectors—shows more clearly than any other what 
infinite variety of forms can be developed externally 
by adaptation to different conditions of life, without the 
internal structure and the original form of the body being 
in any way essentially changed. Beetles have probably 
developed out of a branch of the straight-winged Flies, 
from which they differ only in their transformations (larva, 
pupa, etc.) 
The one order of Licking Flies, namely, the interesting 
