92 THOMPSON YATES LABORATORIES REPORT 
The conditions in the Friendly Islands, previously often referred to, may 
perhaps be quoted as an exception to the statement above — that F. diurna is limited 
in its distribution to West Africa — since the embryos cannot be regarded as nocturnal. 
Probably this condition will be found to be much more extensively distributed. 
On the other hand we have described the embryos of F. loa as very similar to 
those of F. nocturna : but on closer study some points of difference may be noted 
in the disposition and number of the spots. Such a close resemblance indicates either 
that they are identical with F. diurna and that, therefore, F. loa is the parent form of 
F. diurna, or that, being very much alike in all other respects except in the matter 
of the spots as just mentioned, they are intended for a more or less similar life 
history in their intermediary hosts. 
To sum up, although the weight of evidence is on the side of the identity of 
F. nocturna and F. diurna^ there are many points which remain to be cleared up before 
the question can be settled. The F. loa has introduced a serious difficulty into the 
subject, and it appears to us that a solution of the mystery can only be obtained 
when the embryos in a pure case of F. diurna have been successfully and completely 
cultivated in their intermediary' host — which is still to be discovered — to the final 
larval stage, and perhaps it may become necessary to perform experiments of infection 
of man by the use of infected intermediary hosts before a complete solution is 
procured. 
