INSECTA 509 



resulting from the acephalous larva, on the other hand, is coarctate, 

 the last larval skin being retained as a protective puparium, tracheal 

 connections maintaining contact between the pupa within and the 

 larval skin outside it. Final emergence of the fly in this case clearly 

 involves two processes, {a) the liberation of the fly from its pupal skin, 

 and (b) its further liberation from the puparium. The latter splits 

 transversely (Fig. 349 B), the top being thrust away by an eversible 

 head sac, xhtptilinum^ which such flies possess. The features of meta- 

 morphosis just described are characteristic of many flies and by de- 

 fining one of the suborders constitute an important basis of modern 

 classifications (Fig. 349 C). 



The suborder Orthorrhapha includes all those flies which are liber- 

 ated by means of a longitudinal split in the mid-dorsal line of the 

 pupal case. Such flies possess no ptilinum. Many of these, the Ne- 

 matocera, have slender antennae and usually pendulous maxillary 

 palpi. Their larvae are eucephalous with horizontally biting mandibles 

 and their pupae are free. To this series belong the Crane-flies (Fig. 

 3 50 A) , the larvae of which often damage cereal crops by devouring their 

 roots. The Culicidae (Fig. 347) are the gnats and mosquitoes, the 

 piercing proboscis of which has already been described. They are 

 further distinguished by their wings which are fringed with scales. 

 Both larvae and pupae are aquatic, the former being metapneustic, 

 the latter propneustic (with anterior spiracles only). With the blood- 

 sucking habit of these flies has evolved an association with certain 

 organisms which when transmitted to man cause disease. Anopheles 

 is concerned with the transmission of malaria. Stegomyia transmits 

 the causative organism of Yellow Fever while Culexfatigans, a widely 

 distributed tropical form, is a carrier of the thread-worm Filaria 

 bancrofti^ the cause of elephantiasis. 



Nearly related to these are the Chironomidae (midges), the mouth 

 parts of many of which are not adapted for piercing and sucking. A 

 few of these, however, do suck blood, e.g. the midges of the genus 

 Forcipomyia, whose larvae breed, some in water, others behind the 

 bark of trees. 



The Cecidomyidae (Fig. 350 C) are the gall-midges distinguished by 

 their beaded antennae adorned with whorls of setae. The larvae of a 

 few of these are parasitic. Some are predaceous, but others, forming 

 a large majority, are phytophagous, forming galls in plant tissues, e.g. 

 of grasses. Contarinia pyrivora is the pear midge, the larvae pf which 

 develop in the flowers of the pear so as to abort fruit production. 

 Miastor lives behind tree bark in the larval state and as mentioned 

 above is noteworthy for the phenomenon of paedogenetic partheno- 

 genesis. 



Another family of blood-sucking flies, known as the Simuliidaef 



