ENTOMOLOGY 893 
(Guyot). The adult of this parasite lives preferably in the subcutaneous tissues 
of man, producing the so-called Calabar swellings. The embryos, originally 
described as Microfilaria diurna, swim in the blood. Manson, in 1895, suggested 
that they might be carried by Chrysops dimidiata v. d. Wulp; but Leiper, in 
Nigeria, was the first to carry out experiments. Of several biting insects which 
Leiper tried, Chrysops dimidiata and C. silacea were the only ones in which he 
observed a rapid and uniform development of the embryos after feeding the flies 
upon an infected patient. In Haematopota cordigera and Hippocentrum tri- 
maculatum a slight degree of infection was obtained, but development was unequal 
and slow.! Kleine, in Cameroon, found 5.3 per cent of wild Chrysops silacea 
and C. dimidiata infected with larvae of a Filaria, which he believed to belong 
to Loa loa, without proving it by experiment.’ 
The entire life-cycle of Loa loa was completely and brilliantly elucidated 
by Dr. A. and Mrs. §. L. M. Connal, in Nigeria. In dissecting 2,283 wild 
specimens of Chrysops silacea (2,031) and C. dimidiata (252), these investigators 
found twenty-two flies (16 C. silacea, or 0.8 per cent; 6 C. dimidiata, or 2.4 per 
cent; total percentage, 0.96) infected with filariae. They later succeeded in in- 
fecting wild flies of these two species with embryos of Loa loa from man and in 
transmitting the parasite with these flies to guinea pigs, rabbits and a monkey. 
The flies become infective in from ten to twelve days after ingesting the em- 
bryos. It is of interest to note that Chrysops is a strictly diurnal biter, while 
the larvae of Loa loa are, as a rule, found in the peripheral circulation of man 
during the day only. 
Key To THE SPECIES OF Chrysops OF THE BELGIAN CONGO 
1. Apical half of the wing more or less uniformly infuscated, although with paler or more 
yellowish areas or very gradually fading toward the hind-margin; the median dark 
band not sharply divided by a hyaline streak or triangle from the apical spot.... 2. 
Median dark cross-band of wing sharply divided by a hyaline streak or triangle from the 
Sa ea RR NM eon e = ide Nene Selo Nios xi KG AS OG tis. the fone s wala hia wile ROR aca wi 5. 
2. Antennae moderately elongate, slightly shorter than the dorsum of the thorax; first 
segment swollen, thicker than the second; second about half as long as the third; 
basal division of third segment with a sharply constricted basal portion and the 
remainder superficially divided into annuli. Fore tibiae slender. Head and thorax 
1 Leiper, R. T. 1913. ‘Filarza loa.’ Brit. Med. Jl., I, pp. 39-40. 
1913. ‘Report of the helminthologist, London School of Tropical Medicine, for the half-year ending 
April 30th, 1913.’ Report to the Advisory Committee of the Tropical Diseases Research Fund. (Ab- 
stract in Tropical Dis. Bull., II, 1913, pp. 195-196). 
2 Kleine, F. K. 1915. ‘Die Uebertragung von Filarien durch Chrysops.’ Zeitschr. Hyg. Infektionskr., 
LXXX, pp. 345-349. 
3 Connal, A. 1921. ‘Observations on Filaria in Chrysops from West Africa.’ Trans. R. Soe. 
Trop. Med. Hyg., XIV, 6, pp. 108-109. 
Connal, A. and Connal, 8. L. M. 1921. ‘A preliminary note on the development of Loa loa (Guyot) 
in Chrysops silacea (Austen).’ loc. cit., XV, pp. 131-134. 
1922. ‘The development of Loa loa (Guyot) in Chrysops silacea (Austen) and in Chrysops dimidiata 
(van der Wulp).’ loc. cit., XVI, pp. 64-89, 5 Pls. (Correction in 1923, loc. cit., XVI, 7, p. 437). 
4 Ringenbach and Guyomarc’h (1914, Bull. Soc. Path. Exot., Paris, VII, p. 623), in the French 
Congo, found in the stomach of Chrysops centurionis Austen embryos of filariae which they refer to Loa 
loa and Acanthocheilonema perstans, but they were unable to confirm these identifications by experiments. 
Chrysops longicornis has also been included in some of the compilations of the intermediate hosts of 
helminths; but I have been unable to trace original observations or experiments dealing with this insect 
and Loa loa. 
