V.OLUME XIII 
JUNE, 1921 
No. 2 
ON THE LIFE-HISTORY OF IlELICOSPORIDIUM 
PARASITICUM , N.G., N.SP., A NEW TYPE OF PRO¬ 
TEST PARASITIC IN THE LARVA OF DASYHELEA 
OBSCURA WINN. (DIPTERA, CERATOPOGONTDAE) 
AND IN SOME OTHER ARTHROPODS. 
By D. KEILIN, Sc.D. 
Beit Memorial Research Fellow. 
(From the Quick Laboratory , University of Cambridge.) 
(With Plates IV—VI and 5 Text-figs.) 4 
CONTENTS. 
PAGE 
I. Principal host of Helicosporidium and its infection ... 97 
II. Life-history of Helicosporidium parasiticum ..... 99 
1. Localisation of the parasite ...... 99 
2. Early stages and schizogony ...... 99 
3. Formation and structure of spores ..... 100 
4. Development of spores subsequent to the death of the host 102 
5. Supposed mode of infection of the host .... 105 
6. Frequency of infection of Dasyhelea larvae . . . 105 
7. Stages of the host susceptible to infection . . . 106 
III. Other hosts of Helicosporidium parasiticum .... 106 
1. Mycetobia pallipes Mg. (Diptera, Rhyphidae) . . . 106 
2. Hericia hericia (Robin), Kramer, 1899 (Acarina, Tyrogly- 
phidae) ......... 107 
IV. Systematic position of the genus Helicosporidium compared with 
(1) Cnidosporidia, (2) Haplosporidia, (3) Serumsporidia, and 
(4) Mycetozoa. ........ 108 
V. Conclusions .......... 110 
VI. References . . . . . . . . . . Ill 
VII. Explanation of Plates . . . . . . . . 112 
I. Principal Host of Helicosporidium and its Infection. 
The usual host of this new parasite, Helicosporidium parasiticum , is the larva 
of a Ceratopogonid, Dasyhelea obscura Winnertz, which lives in the decom¬ 
posed sap filling the wounds of trees—elm and horse-chestnut. All the material 
used for this study was derived from the wounds of two trees only: (1) an elm 
tree standing on the Caius College ground at Newnham, facing Church Rate 
Parasitology xm 
i 
