490 DIPTERA CHAP. 



few species known, and all of them are rare ; l in Britain we 

 have but two (Ogcodes gibbosus, Acrocera globulus}. The genus 

 Pterodontia, found in North America and Australia, an inflated 

 bladder -like form with a minute head, is 

 amongst the most extraordinary of all the 

 forms of Diptera. The habits are very 

 peculiar, the larvae, so far as known, all 

 living as parasites within the bodies of 

 spiders or in their egg-bags. It appears, 

 however, that the flies do not oviposit in 

 appropriate places, but place their eggs on 

 FIG. 234. Megalylus gm- stems of plants, and the young larvae have 

 -r 7*V A T ida ,'l to find their way to the spiders. Brauer has 



Chili. (After West wood.) 



described the larva of the European Asto- 



mella lindeni? which lives in the body of a spider, Cteniza 

 ariana ; it is amphipneustic and maggot-like, the head being 

 extremely small. The larva leaves the body of the spider for 

 pupation ; the pupa is much arched, and the head is destitute of 

 the peculiar armature of the Bombyliidae, but has a serrate ridge 

 on the thorax. Emerton found the larvae of an Acrocera in the 

 webs of a common North American spider, Amaurobius sylvestris, 

 they having eaten, it was supposed, the makers of the cobwebs. 



Fam. 22. Lcnchopteridae. Small, slender flies, with pointed 

 wings, short, porrect antennae, with a simple, circular third joint, 

 bearing a bristle ; empodium very small, pulvilli absent. Only one 

 genus of these little flies is known, but it is apparently widely 

 distributed, and its members are common Insects. They have 

 the appearance of Acalyptrate Muscidae, and the nervuration of 

 the wing is somewhat similar, the nervures being simple and 

 parallel, and the minute cross -nervures placed near the base. 

 The systematic position is somewhat doubtful, and the meta- 

 morphoses are but incompletely known, very little having been 

 added to what was discovered by Sir John Lubbock in 1862. 3 

 The larva lives on the earth under vegetable matter ; it is very 

 transparent, amphipneustic, with a peculiar head, and with fringes 

 on the margins. This larva changes to a semi-pupa or apterous 

 maggot-like form, within the larval skin ; the true pupa was 



1 For figures, etc., cf. Westwood, Tr. ent. Soc. London, 1876, p. 507, pis. v. vi. 



2 Verh. Ges. Wicn, xix. 1869, p. 737, pi. xiii. 



3 Tr. ent. Soc. London (3) i. 1862, p. 338, pi. xi. 



