PARASITES OF FLIES 241 



" Linear cylindrical, faintly striated transversely, gradually diminishing towards 

 the head, which is obtuse, and furnished with 4 papilloe at a little distance from the 

 mouth, two above and two below ; diminishing towards the tail, which is short and 

 terminated by a dilated round extremity covered by short spines. Mouth in the 

 centre of the anterioi extremity. Anal orifice at the root of the tail." 



General! (1886), Hewitt (1910, p. 381) and Ransom (quoted 

 by Howard, 1911, p. 73) all describe a similar worm, which is 

 now placed in the genus Habronema. Plana noticed that at 

 certain seasons of the year 20-30^0 of flies in Italy might be 

 infected, but Hewitt in England very rarely found infected flies. 

 Ransom in the United States found the worm, mainly in the 

 head, in nine out of thirty-four flies. Although he examined 

 larvae and pupai for these worms with negative results he 

 says " that infection with H. miiscce is acquired during some 

 stage prior to the imago is proved by the discovery of the 

 parasites in a fly caught just as it was emerging from the pupa." 

 Since that time Ransom (191 1) has further investigated the 

 subject, and has apparently worked out the life-cycle of the para- 

 site. It appears that the worm lives in the stomach of the 

 horse, and that the embryos which pass out in the faeces enter 

 the fly larvae. When the flies emerge the larvae are full-grown, 

 but have to pass into the intestinal canal of the horse before 

 reaching maturity. 



The writer has examined several hundreds of Stomoxys, 

 caught in various places, for similar worms, but has only found 

 them in flies caught close to a certain farm near Cambridge. In 

 1908 4"3Vo were found to be infected, 9^/0 in 1909, 13% in 1910, 

 and io7o in 19 H- 



The degree of infection may be judged by a detailed account 

 of the findings in 115 flies caught on July 15th, 191 1. Each fly 

 was carefully dissected, the proboscis, head, thoracic and leg 

 muscles and abdomen being examined separately. In 100 flies 

 no worms were found. Eight flies were infected with single 

 worms ; in four the worms were in the head, in two in the 

 proboscis, and in two in the thorax. One contained two worms 

 in the thorax, and one three worms in the head. In one fly two 

 worms were found in the thorax and one in the proboscis ; and 

 in another two worms in the thorax, two in the proboscis and one 



G.-s. 16 



