64 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Protozoa. 
New Type of Parasitic Protist in Fly Larvae. — D. Keilin 
(. Parasitology , 1921, 13, 97-113, 3 pis., 5 figs.). In the general 
cavity, fat-body and nervous system of the larva of a fly, Dasyhelea 
obscura, which lives in the decomposed sap filling the wounds of trees — - 
elm and horse-chestnut — Keilin found Helicosporidium parasiticum 
g. et sp. n. It differs from all the actually known Protists, and forms 
a new type which may be temporarily included among Sporozoa. The 
trophic stage has the form of a small round cell, 2-3 //.in diameter, with 
a minute spherical nucleus. There is very active schizogonic multi- 
plication. Schizonts form a small morula of 4 /x in diameter, composed 
of four or eight merozoites, which become free. The spore, 5-6 //. 
in diameter, is composed of four cells surrounded by a thin wall or 
sporocyst. Of the four cells, three, which are the real sporozoites, are 
discoidal and occupy the centre of the spore. The fourth cell forms a 
peripheral spiral filament surrounding the three central cells. The 
spores open inside the dead body of their host by the unrolling of the 
spiral filameut, and the sporozoites are thus liberated. The spiral 
filament when unrolled is 60-65 /x long, pointed at both ends, 1 /x thick 
at its widest portion, and very resistant. Its nucleus is 2-3 //, long and 
lies 15 /x from one end of the filament. The strange parasite occurs 
also in a Dipteron ( Mycetobia pallipes) and a mite ( Hericia hericia ), 
both of which occur in tree wounds. J. A. T. 
Human Coccidiosis. — Frank G. Haughwout {Philippine Journ. 
of Science, 1921, 18, 449-82, 4 pis., 1 fig.). Description of a case of 
infection with Isospora hominis. An account is given of the sporoblast 
formation, the sporozoites, the development of the cysts, and so on. 
The parasite enters the alimentary tract in encysted form. There are 
two tetrazoic spores, there being eight sporozoites formed in each case. 
In the intestine the vermiform sporozoites emerge from their containing 
cysts and invade the epithelial cells of the mucosa of the small intestine. 
They are obligatory epithelial-cell parasites. Within the host cell the 
sporozoites develop into trophozoites, which grow at the expense of the 
protoplasm of the cell. When the food supply is exhausted and the 
trophozoite has attained full growth, the nucleus undergoes multiple 
division (schizogony) and with plastogamy a number of daughter cells, 
or merozoites, are. formed. These escape from the host cell and enter 
the lumen of the intestine to seek new host cells. Those that are 
successful develop in their turn into trophozoites which also undergo 
schizogony. This asexual cycle is repeated a variable number of times, 
and finally changes take place leading to a sexual process (sporogony), 
which is initiated by a process of fertilization involving the union of 
sexually differentiated gametes. This is followed by the encvstation of 
the zygote, which then passes out with the faeces and completes its 
development in the outer world. In the course of time the whole race 
undergoes sporogony and the host is clear. J. A. T. 
