38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I25 



existed above and below the onchocerciasis zone as well as within it, 

 there were two species of black flies that seemed to be most numerous 

 within the altitude belt in which the disease was most prevalent. He 

 therefore correctly surmised that the black flies were the probable 

 vectors. Unfortunately, he did not carry out further investigations to 

 verify his hypothesis. 



Macfie and Corson (1922) got negative results with Glossina pal- 

 palis and G. longipalpis fed on infected persons. Dissections of 100 

 specimens of Pediciilus humanus yielded no filariid larvae. Twenty 

 lice taken from a noninfected individual were permitted to feed on 

 persons harboring larvae of both 0. volvulus and Acanthocheilonema 

 Persians. Only larvae of the latter were found upon dissection, sug- 

 gesting that lice could only ingest the blood-inhabiting microfilariae 

 and not those in the skin (O. volvulus). Blanchard and Laigret 

 (1924) fed Ornithodorus mouhata, Chnex lectularius, Auchmeromyia 

 luteola (Congo floor maggot), Simulium spp., and leeches (unidenti- 

 fied) on infected individuals. All these took up microfilariae, but only 

 in the tick did the larvae remain alive. Akhough the microfilariae re- 

 mained viable in the ticks up to 12 days, they did not undergo develop- 

 ment. The simuhids also ingested large numbers of microfilariae, but 

 their rapid death (after one day) terminated further observations. 



Blacklock (i926a,b), working in Sierra Leone, Africa, noted that 

 persons heavily infected with microfilariae of O. volvulus in the skin 

 had no larvae in their blood. He reasoned that if a blood-sucking 

 arthropod was the vector, it was one that had to rasp and tear the skin 

 in order to reach the blood, thus dislodging the larvae that would then 

 be ingested with the blood. In his early experiments with Glossina 

 palpalis, Auchmeromyia luteola, and Simulium damnosum, results 

 were negative. In later, large-scale investigations carried out in 1925 

 he successfully infected wild-caught .S". damnosum on infected patients, 

 and for the first time traced the subsequent development of the para- 

 sites in the gut, thorax, head, and proboscis of the flies. Infective 

 larvae were found in the proboscis as early as 7 days after the in- 

 fective meal. 



Sharp (1927), in Nigeria, fed 6*. damnosum on a person infected 

 with microfilariae of both Onchocerca volvulus and Dipetalonema 

 streptocerca (also skin-inhabiting) in the proportion of 1:5. One 

 hour after exposure he found microfilariae of both species in the 

 stomach of the flies, but O. volvulus predominated 10: i, indicating 

 that the flies had selectively ingested O. volvulus in preference to D. 

 streptocerca. By the third day O. volvulus had migrated to the thorax 

 and had transformed to the "sausage" stage, while very few D. strep- 



