MALARIA EXPEDITION TO NIGERIA 91 
towns which we visited, and especially of the Kroo boy gangs in the towns of 
Southern Nigeria. Moreover, we often observed, especially in those towns where 
civilisation was very backward, the natives asleep during the middle hot part of the 
day ; indeed, the Kroo boy in English Government employ steals a mid-day nap 
whenever he can. These habits have been practised, no doubt, for generations, and 
probably were prevalent to a much greater extent for years before the influence of 
Europeans was felt. Such conditions would, in a great measure, account for the 
variety in the cases of filarial infection we met with in West Africa, and which 
Thorpe observed in the Friendly Islands, and point strongly to the identity of the 
two embryos, or rather to the phenomenon of the accommodation of the one or the 
other or of an original embryo perhaps exhibiting no periodicity whatever, to the 
varying habits of the natives who formed their habitat. 
The intermediary host. F. nocturna has been successfully cultivated in several 
species of mosquitoes of both genera. In West Africa, after several attempts, we 
were able to cultivate this embryo in Anopheles cos talis; but all our efforts to cultivate 
F. diurna failed. But this is not remarkable, for, if F. diurna had been evolved in 
consequence of the habits of the natives, it is not unnatural to expect that its 
intermediary host is an insect, probably a mosquito, not essentially nocturnal in its 
habits such as A. costalis, but one whose habits are diurnal. 
Analogy with avian filariasis. In the chapter on Avian filariasis we describe 
eleven new species of filariae, each having a different embryo ; in fact, we were soon 
able after a little practice to decide the species of the worm even by a study of the 
stained specimen of the embryo. Each species then possesses distinct adults, which 
give rise to a characteristic embryo. This would suggest a similar condition among 
human filariae, and thus that F. diurna and F. nocturna, being indistinguishable in 
fresh and stained specimens, have a common adult form. 
The adult form. The adult of F. nocturna is well known — F. bancrofti. The 
adult of F. diurna has not yet been described, unless F. loa be that form. Now, the 
distribution of F. loa is, as far as we can ascertain, limited to the West Coast of 
Africa, and Manson makes the same statement. It has not been met with in any 
other part of the world,* and the occurrence of a worm of the length of F. loa 
occurring under the conjunctiva of the eye, cannot possibly have been overlooked 
anywhere. 
F. diurna, as far as we at present know, is also apparently limited to the 
West Coast of Africa, and has been found in some cases of natives in which F. loa 
has been removed from the eye — although this is not remarkable as anything more 
than an ordinary coincidence, considering the prevalence of F. diurna cases on the 
Coast. Moreover cases of F. loa have occurred in which no embryos could be 
demonstrated in the blood. 
* Stossich states that it occurs in the Antilles and Guiana, but Manson says, in his latest edition of Tropical Diseases, 1900, 
'it is peculiar to the West Coast of Africa.' 
