D. Keilin 
111 
H elicosporidium n. g. 
Diagnosis. Parasitic protist; trophic stage in the form of a small round 
cell 2-3 g in diameter, with small spherical nucleus. Schizogonic multiplication 
very active. Schizonts forming a small morula of 4/x in diameter, composed 
of four or eight merozoites, which become free. 
Spore (5-6/x in diameter) is composed of four cells surrounded by a thin 
wall or sporocyst. Of the four cells, three, which form the real sporozoites, are 
discoidal, occupying the centre of the spore. The fourth cell forms a peripheral 
spiral filament which surrounds the central cells. 
The spores open inside the dead body of their host, bv the unrolling of 
the spiral filament, and the sporozoites are thus liberated. 
The spiral filament when unrolled is 60-65 /x long, pointed at both ends 
and 1/x thick at its widest portion; its nucleus 2-3/x long, lies 15/x from one 
end of the filament. This filament is of a very resistant nature. One species 
known. 
Helicosporidium parasiticum n. sp. 
Diagnosis. The same as that of the genus. 
Habitat. Body cavity, fat body and nervous system of the larva of 
Dasyhelea obscura Winnertz (Diptera, Nematocera, Ceratopogonidae). Occurs 
also in Mycetobia pallipes Meig. (Diptera, Nematocera, Rhvphidae) and in 
Hericia hericia (Robin), Kramer, 1899 (Acarina, Tyroglyphidae). The hosts 
inhabit wounds of elm and horse-chestnut trees, Cambridge, England. 
Acknowledgements. I am much indebted to Mr L. E. Robinson, who is 
engaged in research in the Quick Laboratory, for the very friendly help that 
he has given me in the preparation of this paper for the press and especially 
for the great pains he took in the preparation of the accompanying photo¬ 
micrographs (PI. V). 
REFERENCES. 
Caullery, M. and Mesnil, F. (1905). Recherches sur les Haplosporidies. Arch. Zool. 
Exper. iv. 101-180. Pis. XI-XIII. 
Doflein, F. (1916). Lehrbuch der Protozoenkunde, iv ed. Jena. See pp. 997-1009. 
Ikeda Ivaji (1912). Studies on some Sporozoan of Sipunculoides. I. The life-history of a 
new Actinomyxidian, Tetractinomyxon intermedium g. et sp. nov. Arch. f. Protist. xxv. 
241-272. PI. X. 
Keilin, D. (1920 a). On a new Saccharomycete Monosporella unicuspidata gen. n. nom., 
n. sp. parasitic in the body cavity of a Dipterous larva (Dasyhelea obscura Winnertz). 
Parasitology, xn. 83-91. 
- (1920 6). On two new Gregarines, Allantocystis dasylielei n. g., n. sp., and Dendro- 
rhynchus system, n. g., n. sp. parasitic in the alimentary canal of the Dipterous larvae, 
Dasyhelea obscura Winn, and Systenus sp. Parasitology, xii. 154-158. PI. X. 
Michael, A. (1903). British Tyroglyphidae, London; Ray Society, Vol. n. See pp. 31-38. 
Pis. XXIII-XXIV. 
Pfeiffer, L. (1895). Die Protozoen als Krankheitserreger. Nachtrage I. Ueber Blutparasiten 
(Serumsporidien) bei blutkorperchenfreien niederen Thicren, pp. 9-26. G. Fisher, Jena. 
Robin, Ch. (1868). Recherches sur une espece nouvelle de Sarcoptides du genre Glyciphage. 
Journ. Anat. Physiol, v, 603-625. 
