DOLlCHOPODIDyE. 
607 
appearance of these flies are the remarkable structures often found in the 
male, apparently for the purpose of impressing the opposite sex, 
and taking the form of curious elaborations of the feet, head and 
wings. 
The sexes are easily distinguished, apart from these ornamental 
characters, by the form of the genital organs, the male claspers being 
very large and complex, generally pointing forwards and lying along the 
under side of the abdomen ; since the sexes of the same species often 
differ a good deal in general character it is advisable to take every op¬ 
portunity of securing male and female together when found pairing. As 
a rule the metallic coloration of these flies renders their identification easy, 
but a good many forms lack this distinguishing mark and are dully 
coloured. In these cases they are very apt to be confused with some of 
the Acalyptrate Muscoids, especially the Ephydridce , whose general 
characters are often curiously similar. These, however, lack the rows of 
thoracic bristles, and the venation of the wings is usually slightly 
different, the 1st basal cell being longer than in the Dolichopodidce. 
The head and mouth in the Ephydrids is also generally larger, and they 
have not the row of bristles round the hind edge of the eye possessed by 
Dolichopodids. Both families are predaceous, and both favour damp 
situations. Ephydrids are commonly found walking on the surface 
of water, and some Dolichopodids are also able to perform this feat. 
Both groups contain species in which the front femora are thickened 
and armed with spines on the under side. 
This striking likeness would seem to indicate some close genetic 
relationship, but this is improbable if we accept the principles of classi¬ 
fication in general use, and it is more likely that the resemblances are due 
to the similar mode of life of the two groups : either the surroundings 
and habits of the insect influence its form in some unexplained way, 
or a certain pattern is found to pay best in these surroundings, and the 
variations in the direction of this pattern have become perpetuated. 
Very little is known of the life-history. The larvae (fig. 399) are amphi- 
pneustic, slender and cylindrical, and live in the exuding sap or 
under the bark of trees, or in decaying vegetable matter. Their diet is 
uncertain. The pupae are generally free ; their abdominal spiracles are 
very small, and the breathing is done through two long horns which bear 
the thoracic spiracles. 
