326 MEDICAL ENTOMOLOGY 



nearly always infected with Herpetomonas luciliae, Roubaud, and with 

 Rhynchoidomonas luciliae, Patton, which is parasitic in its Malpighian 

 tubes. 



GENUS PYCNOSOMA, BRAUER AND BERGENSTAMM 



Closely allied to Lucilia. Cheeks usually of a buff or orange red. 

 Posterior dorsocentral and acrostichal bristles well developed. Sterno- 

 pleural bristles only two in number, arranged 1:1. 



The flies of this genus are the Oriental representatives of the genus 

 Chrysomyia, and are by some Dipterologists included with them. They 

 are thick-set insects and have characteristic red cheeks. In tropical coun- 

 tries they are abundant about night soil trenches and slaughter houses ; 

 as they frequently alight on food they may be the disseminators of dis- 

 ease-causing bacteria. Pycnosoma marginale Wied., is a common pest 

 in the Soudan, and is widely distributed in Africa, being abundant in the 

 Transvaal and Natal. Pynnosoma putorium, Wied., is common in West 

 Africa, while P. flaviceps, Walk. , is common in South India. 



GENUS CHRYSOMYIA, FABR. 



Medium-sized bright metallic flies, with three longitudinal stripes 

 on the thorax. Thoracic bristles as a rule poorly developed and often 

 inconstant. Sternopleural bristles three in number and arranged 2:1. 



The flies of this genus are restricted to America and the West Indies, 

 and the best known, C. maceallria, Fabr., is the ' Screw Worm fly ', 

 the larvae of which cause serious myiais in man and animals in 

 Cuba, Brazil and other parts of Tropical America. The species are 

 chiefly distinguished from Pycnosoma by the number and arrangement 

 of the Sternopleural bristles. 



Chrysomyia maceallria is of a metallic blue to green colour, with 

 three black longitudinal stripes on the thorax ; the abdomen is covered 

 with dark hairs. The legs are black and the wings transparent. It 

 measures from 8 to 10 mm. in length. 



Its larva is of a dirty white colour and consists of twelve segments, 

 each of which is furnished with one or more circlets of spines on its 

 upper border ; the first has two, sometimes three, the second and third 

 three each, and there are four on the other segments. The puparium is 

 dark brown and has rudimentary spines. 



Chrysomyia maceUaria will lay its eggs on any part of the body which 

 has been injured, and is readily attracted to a bleeding surface. It will 



