Rogers, who, on comparing it with Herpetomonas muscae domesticae, as figured by Prowazek, recognized the close similarity in the build of the two flagellates. Unfortunately, Prowazek erroneously described the adult flagellate of H. muscae domesticae as possessing two flagella closely united together, and, in addition, its life-cycle according to his account is exceedingly complicated. For more than a year I have made an exhaustive study of this flagellate, the type species of the genus Herpetomonas. In Madras about 100 per cent, of flies, caught in the bazaar meat shops, are infected with it, and as a result of my observations on the living parasite as well as in stained preparations, I am unable to accept Prowazek's view of its flagellar apparatus, for I find the adult flagellate has a single flagellum. I can only assume that Prowazek happened to examine flies in which the majority of the adult flagellates were undergoing the early stages of simple longitudinal division; I have frequently seen this in Madras. I also find that the life-cycle of the flagellate of the house-fly is very simple, and is similar to that of the parasite of kala-azar so far as we know it at present.
You will remember Prowazek began his description of H. muscae domesticae at its adult flagellate stage, and entirely omitted the stage preceding it, thus giving anyone who read his paper an entirely erroneous idea of its life-cycle. As you will see later, the earlier stages in the development of the parasite are of great importance, as it is then when it is so like the parasite of kala-azar.
In order, therefore, to clear up this difficulty I will describe in some detail the life-history of H. muscae domesticae, the complete account of which I shall reserve for another occasion. After having studied a large number of these parasites I have found it convenient
