Filar ia loa 29 



when immature, in the eye ; and in a large number of cases, 

 immature nematodes of unrecognized species, often belonging to 

 the genus Filaria^ have been removed from this organ. 



The embryonic form circulating in the blood vessels must 

 evidently be removed from the body of the primary host by 

 some species of- blood-sucking insect. Manson thought that by 

 virtue of the appearance of these embryos in the peripheral cir- 

 culation during the daytime some day-biting insect must be 

 responsible for the transfer. He suggested the Mangrove fly, 

 Chrysops diniidiatus v, d. Wulp., a common form in the region 

 in question. These conclusions were attacked by Annett, Button, 

 and Elliott (1901) without their being in position to furnish any 

 very decisive evidence for the view they advance of the identity 

 of F. diuriia and F. nocturna. More recently Brumpt has 

 brought forward strong evidence in favor of Manson's view in 

 that he has discovered embryos of F. diurna in the circulating 

 blood and identical forms in an adult female F. loa from the 

 same host. He noted also that the embr}'0s were constantly 

 present in the peripheral circulation, even though more abun- 

 dant by day than by night. The effort to discover the inter- 

 mediate host in a species of Glossina was unsuccessful. If the 

 observation of Brumpt that embryos are constantly present in 

 the peripheral circulation is confirmed, then it is evident that 

 the intermediate host may be a mosquito, as in the case of other 

 species of Filaria. Annett, Button, and Elliott found that Ano- 

 pheles costalis seiwed in West Africa as intermediate host for 

 F. Bancrofti but not for F. diurna. This observation will not 

 exclude other mosquitos also ; however, it does speak strongly 

 against their view of the identity of these two microfilariae. 



Whatever may be the precise character of the intermediate 

 host, of the changes passed through by the embryo filaria within 

 it, and of the method by which it is introduced into the human 

 body again, it is evident that the actively migrating F. loa, that 

 form best known from cases on record, is the semi-adult worm. 

 In some cases this has appeared within about one year after the 

 host has entered infected territory and in other cases as much 

 as five, eleven, or even thirteen years have elapsed since leaving 



299 



