154 
ON TWO NEW GREGARINES, ALLANTOCYSTIS DASY- 
HELEI N.G., N.SP., AND DENDRORHYNCHUS SYSTENI 
N.G., N.SP., PARASITIC IN THE ALIMENTARY CANAL 
OF THE DIPTEROUS LARVAE, DASYHELEA OBSCURA 
WINN. AND SYSTENUS SP. 
By D. KEILIN, Sc.D. 
Beit Memorial Research Fellow. 
(From the Quick Laboratory , University of Cambridge.) 
(With Plate X and 2 Text-figures.) 
1. ALLANTOCYSTIS DASYHELEI n.g., n.sp. 
The host of this gregarine is the larva of a Ceratopogonid: Dasyhelea obscura 
Winnertz, which, as I have previously mentioned 1 , lives in the decomposed 
sap filling the infected wounds of the Elm and Horse-chestnut trees in Cam¬ 
bridge (at Newnham and along the Queen’s Road). The parasitised larvae 
were found late in the season, about the end of September, they were all 
young and never heavily infected, containing from three to eight and excep¬ 
tionally twelve parasites in different developmental stages. The gregarine 
seems to be rare as among several hundred of these larvae examined only 
twelve yielded this interesting parasite. 
All the stages of Allantocystis dasyhelei occur in the midgut of its host, 
in the space between the intestinal epithelium and the peritrophic tube, and 
they always lie with their main axis parallel to that of the larva. 
The full-grown sporont is elongated, 65-75 y long and 20-22 y across its 
widest portion (PI. X, fig. 3). The sporont moves slowly and its body easily 
bends on meeting an obstacle. The ectoplasmic layer is very thin except 
anteriorly. The endoplasm is very granular and completely masks the nucleus, 
which can be detected, however, by compressing or staining the parasite; 
the nucleus then shows a structure typical of gregarines, i.e. a large vesicle 
with a distinct karyosome. The youngest stages of the parasite observed were 
the sporonts, 25-35 y in length, differing from the full-grown forms only in 
having their endoplasm less granular and in containing several patches of 
very small yellowish granules (PI. X, figs. 1 and 2). In sexual association the 
gregarines attach themselves to one another by their anterior extremities. 
1 See D. Keilin, Parasitology, this volume, p. 85. 
