that this parasite is a hsemocytozoon can no longer be entertained, and Christophers' recent studies on the extracorporeal life-cycle of Piroplasma canis in the tick have shown that it does not pass through a flagellate stage similar to that of the parasite of kala-azar. I am aware that certain observers claim to have discovered flagellate stages in some Piroplasmata; their observations, however, are far from convincing. I have recently seen some of these so-called piroplasma flagellates, and have no hesitation in saying that they do not bear any resemblance to the characteristic flagellates of the parasite of kala-azar. It should also be noted that these flagellate stages of Piroplasmata have so far only been seen in test-tubes or in the blood of the vertebrate host, whereas they ought to occur naturally in ticks or other invertebrates.
There is, however, no doubt that the parasite of kala-azar and its two allies, as seen in man, are but stages in the life-histories of flagellates, and the important question to answer is, do they belong to any known group of the parasitic flagellata? As our knowledge of the life-cycles of these organisms is exceedingly limited, I think it somewhat premature to say they belong to an entirely new genus, and I hope to show you that they do belong to a group which has long been recognized as occurring in the alimentary tracts of insects. From a study of the flagellates of the parasite of kala-azar in the test-tube, as well as in the bed-bug Cimex rotundatus, I have no hesitation in saying it is not a trypanosome; for, like all other observers who have studied this stage, I have never seen anything similar to the well-known vertebrate trypanosome.
The most important suggestion as to the nature of the parasite of kala-azar was undoubtedly made by
