1 84 THOMPSON YATES LABORATORIES REPORT 
It is this last group which claims our attention at present. The diagrams are 
meant to illustrate a discourse delivered by one of us at the Royal Institution {Pro- 
ceedings of the Roy. Inst., 1900, and also Nature, March 29, 1900) ; but we shall 
now give a description sufficient to enable the reader to follow the life-history from 
this paper alone. The figures show the appearance of the parasites as seen in unstained 
preparations — the cytology of some of the stages (Figs. 53-60) in the gnat not yet 
being sufficiently established to warrant illustration in a scheme of this kind. 
We adopt the name Haemamoebidae, Wasielewsky, for the whole group. At 
least three species occur in human beings (producing the difFerent varieties of malarial 
fever) ; one species in monkeys, three in bats, and two in birds. We illustrate only 
the species found in man and birds, those of monkeys and bats being closely similar 
to the human species, but, so far as we know at present, not identical. The develop- 
ment of four of the species has been followed in gnats. The three human species 
develop in gnats of the genus Anopheles, while one of the avian species (Haemamoeba 
relicta) lives in gnats of the Culex pipiens type. The insect hosts of the remaining 
species have not as yet been found. 
So far as we know, the life-history of all the species is practically identical, 
and is as follows : — The youngest parasites are found as minute amoebulae living 
within or upon the red corpuscles of the vertebrate hosts. Each contains a nucleus, 
which stains by the Romanowsky method. Growing rapidly in size, the amoebulae 
convert the haemoglobin of the containing corpuscles into a varying number of 
brown or black granules, which are called the melanin or malarial pigment. These 
granules lie in the bioplasm of the parasite surrounding the nucleus. After an inter- 
val of from one to several days (according to the species concerned) the amoebulae, 
still contained within the corpuscle, reach maturity, and become either (a) sporocytes 
or (F) gametocytes. In the case of the amoebulae which become sporocytes the nucleus 
divides into a number of segments (varying according to the species). Each segment 
of the nucleus surrounds itself with a portion of the bioplasm, and becomes a spore — 
the process being obviously one of simple asexual propagation. Finally the corpuscle 
which contains the parasite, and which has now been almost entirely destroyed by it 
bursts and liberates the spores, allowing them and a small nucleus de reliquat, consist- 
ing chiefly of the melanin, to fall into the liquor sanguinis. The melanin is taken up 
by the phagocytes of the host, while the spores attach themselves to fresh red 
corpuscles, become amoebulae in their turn, and thus continue the life of the organisms 
indefinitely within the vertebrate hosts. 
In the case of the amoebulae which become gametocytes the history is quite 
difFerent. It is not yet definitely known what determines a given amoebula to 
become either a sporocyte or a gametocyte, but the fact must be accepted. In the 
gamoetocytes the nucleus does not divide as in the case of the sporocytes — the parasite 
reaches maturity without showing any sign of spore-formation. In the majority of 
