92 A BOOK OF INSECTS 



include our fritillaries and admirals, as well as the 

 famous purple emperor {Apatura iris). Both these sub- 

 families have a world-wide distribution. The Brassohnce 

 are large, robust insects found only in tropical America. 

 The Morpkince are confined to tropical America and the 

 I ndo- Malayan region. Some of the New World species 

 have brilliant blue wings, and are among the most beauti- 

 ful of all butterflies. The four remaining sub-families 

 include a very large number of species, many of which 

 are known to be distasteful to insectivorous creatures. 

 The majority are conspicuously coloured. The Danaince 

 are represented in all the warmer regions of the world, 

 and range far north in America, though not in Europe ; 

 the Acrcv'uxr occur in tropical America, Africa, India 

 and Australia ; while the HcUconiince and Ithomwice are 

 confined to Tropical America. 



Order XVII. — Diptera. 



The true flies, which constitute this order, may be 

 distinguished from all other winged insects by the reduc- 

 tion of the hind-wings to stalked knobs called balancers 

 or halteres, the fore-wings alone being used for flight. 

 In some families there is a membranous hood, called 

 the squama, behind each wing. The mouth-parts are 

 modified for piercing and sucking (page 45). The antennas 

 vary greatly in different families, but are rarely con- 

 spicuous. The legs are usually slender, often spiny, while 

 the tarsi have five segments. The wings are membranous 

 with not more than seven longitudinal nervines, and a 

 few cross nervules. Diptera undergo a very complete 

 metamorphosis, the larva being always eruciform, often 

 a legless maggot. The pupa is variable in form. It is 

 rarely enclosed in a cocoon, but lies buried in the ground, 



