Remarks by Dr. PATRICK MANSON.—I have no hesitation in saying that I consider the communication to which we have just listened from the President to be one of the most important on the subject of filaria loa that has been made for many years. Two or three years ago I had an opportunity of examining the blood of a number of negroes from Old Calabar in a missionary establishment and elsewhere, and I made the interesting discovery that in 50 per cent. the blood contained the embryos of a species of filaria—_Filaria perstans_—which were quite different in their zoological characters from the filaria of the blood, with which every one must now be familiar. While examining one of these patients whose blood contained this new species of filaria I found another species of bloodworm, whose anatomical features were similar to those of the ordinary _Filaria sanguinis_, but which presented a very great difference physiologically, inasmuch as contrary to what is observed with the ordinary filaria, this one disappears at night and can only be found in the blood during the daytime. This second new bloodworm I therefore called _Filaria diurna_. Some time later, in a communication which I had from Professor Leuckart, he told me he had been enabled to examine the embryos in the uterus of an adult _Filaria loa_, and he sent me a sketch of these embryos. On comparing this sketch with the _Filaria diurna_, I came to the conclusion that they were practically identical, and therefore that the filaria I had found in the blood of the negroes might possibly be the embryos of _Filaria loa_. This opinion appeared to me to be strengthened by the fact that this patient had previously had a loa under the conjunctiva. I have very little doubt that the embryo of _Filaria loa_ finds its way into the blood. Clinically, there is no evidence of its attempting to find its way to the surface of the body, and it is evident that there must be some arrangement by which it can get out of the body, and so propagate its species by passing from one person to another. From this and other considerations I consider that it must be by way of the blood that the necessary escape is effected. With the ordinary filaria it is now well known that the mosquito removes it from the blood and acts the part of intermediate host, and I suppose that a similar arrangement must exist in respect of the _Filaria loa_. On inquiring of the Old Calabar negroes as to the blood-sucking insects of the district, I learned that there was a particular fly which exists in great numbers about the creeks, and was very annoying on account of its pertinacity. I think this insect, which is also diurnal in its habits, is probably the intermediate host for the _Filaria loa_, us the mosquito is for the ordinary filaria. I do not believe that this individual worm was the only _Filaria loa_ in the body of the patient whose history we have just listened to. It became visible simply because it wandered