ENTOMOLOGY 851 
all), none of which survived until the next day. The only interesting conclusion 
drawn from these experiments was that the blood-sucking arthropods attract 
the microfilariae scattered in the derm to the point of the bite.! 
The life-cycle of O. volvulus in the insect vector was finally elucidated by 
Blacklock in Sierra Leone. He found that in the Konno District some forty-two 
per cent of the natives showed microfilariae in the skin. The prevalence of 
Eusimulium damnosum being noted at the time, some of these flies were captured 
shortly after they had started feeding upon natives. Upon dissection, of seven 
hundred and eighty flies, twenty (or 2.6 per cent) showed in the gut microfi- 
lariae with all the morphological characters of O. volvulus larvae. Of 1,320 black- 
flies captured in the same manner fifteen (or one per cent) presented in the 
thorax developmental forms of a nematode at various stages. By feeding wild 
flies on selected natives known to harbor O. volvulus and by keeping the flies 
alive as long as possible afterward, the percentage of thorax infections was con- 
siderably increased. In one experiment, of twenty-two flies dissected later than 
two days after biting an infected native, eighteen proved to be infected in the 
thorax. It was also shown that the larvae later migrate from the thorax to the 
head of the fly and that they eventually gather in the labium. On several oc- 
casions the larvae were seen breaking spontaneously through the membranous 
labella at the tip of the labium. It is probably in this fashion that they enter 
the skin of man when an infected fly bites. The complete life-cycle in Husimulium 
damnosum, from the time of feeding on an infected person to the appearance of 
larvae in the labium, was seven days or more, depending upon the temperature.’ 
Some other parasitic infections of man or animals have at one time or other 
been attributed to the bites of black-flies, but without experimental proof. Thus 
Railliet states that Simulidae transmit Setaria equina (Abildgaard), a helminth 
parasite of equines, but gives no evidence in support of this view.? Dry de- 
scribes a filarial infection of man in Kenya Colony which he refers (perhaps in- 
correctly) to Onchocerca volvulus and which, he claims, might be carried by a local 
black-fly, Simuliwm neaver Roubaud.* In certain mountainous areas of Guate- 
mala and southern Mexico, a related helminth, Onchocerca caecutiens Brumpt, 
causes a peculiar dermatosis (‘‘erzsipela de la costa’’), sometimes accompanied 
by ocular trouble. Nothing definite is known regarding its mode of transmission, 
although some biting arthropod is probably the vector. Robles suggests as 
possible carriers two species of black-flies, locally called ‘‘ coffee-flies”? and tenta- 
tively named Simulium samboni Jennings and S. dinellit Jodin.® These are the 
1 Blanchard, M. and Laigret, J. 1924. ‘Recherches sur la transmission d’Onchocerca volvulus par 
divers parasites hématophages.’ Bull. Soc. Path. Exot. Paris, XVII, pp. 409-417. 
2 Blacklock, D. B. 1926. ‘The development of Onchocerca volvulus in Simulium damnosum.’ Ann. 
Trop. Med. Paras., XX, 1, pp. 1-48, Pls. I-IV. 
1926. ‘The further development of Onchocerca volvulus Leuckart in Simulium damnosum Theob.’ 
Ann. Trop. Med. Paras., XX, 2, pp. 203-218, Pl. XIX. 
1927. ‘The insect transmission of Onchocerca volvulus (Leuckart, 1893), the cause of worm nodules 
in man in Africa.’ Brit. Med. Jl., (1927), vol. I, pp. 129-133. 
3 Railliet, A. 1895. ‘Traité de zoologie médicale et agricole.’ 2d. Ed., (Paris). 
4 Dry, F. W. 1921. ‘Trypanosomiasis in the absence of tsetses, and a human disease possibly 
earried by Simulium in Kenya Colony.’ Bull. Ent. Res., XII, pp. 233-238, Pls. VII-VIII. 
5 These identifications are most probably erroneous. 
