D. Keilin 85 
in abundance parasitized by M. bicuspidata. His material was derived from 
a tank at the Jardin des Plantes, Paris. 
The genus Monospora , or, as we shall call it now, Monosporella, has hitherto 
comprised: (a) the species bicuspidata Metschnikoff and (6) a yeast-like 
fungus found by Butchli (1876, p. 148, PL XIV, fig. 8) in the coelom of a 
free-living nematode, Tylenchus pellicidus Bast. Unfortunately this author’s 
description and figures are insufficient for determining more than the genus 
to which the parasite belongs. 
This summer (1919) I found a new species of Monosporella , which I 
propose to name Monosporella unicuspidata , living in a Dipterous larva: 
Dasyhelea obscura Winnertz 1 . The larvae of this Ceratopogonid live usually 
in the thick brown sap which fills the infected wounds of elm or horse-chestnut 
trees. W hilst larvae collected from the wounds of a horse-chestnut, standing 
on the grounds behind the School of Agriculture, Cambridge, harboured 
Monosporella, those taken from elms (at Newnham and along the Backs. 
Cambridge) were not infected by this fungus, they contained however other 
parasites which will be dealt with separately. 
The proportion of larvae infected with M. unicuspidata appeared to be 
low, for but twenty out of several hundred forming the material examined 
by me were found to be infected. The actual proportion of infected individuals 
doubtless varies in nature and it must have been greater in this instance. 
Owing to the larvae being insufficiently transparent to permit the detection 
of the few parasites that may occur in mild forms of infection, some of these 
doubtless escaped notice. It appears probable, moreover, that a number of 
larvae may rid themselves of parasites by phagocytosis as some examples of 
Daphnia do when attacked by few M. bicuspidata. The parasitized larvae 
observed by me belonged to three successive generations of Dasyhelea and 
they were all heavily infected. A parasitized Dasyhelea larva is easily recognized 
b} Che milky appearance of the body and especially of its posterior segments. 
Examined microscopically, the larva shows an enormous number of elongated 
refractive cells, completely filling the body cavity, and in some cases so 
crowded together that they all take a direction parallel to the long axis of 
the body of the larva. In spite of the great number of parasites that are present, 
the larvae are able to move, the fat body seems to be the only organ which is 
completely destroyed, whereby the larva becomes more transparent and the 
parasites are better observed. Finally the larva dies and decomposes rapidly, 
thus setting free the resistant forms of the parasite. In the living larva, even 
when heavily infected, almost all developmental stages of the parasite are 
easily seen by cutting open the larva in a drop of normal salt solution or 
Amman’s lactophenol 2 . 
1 The identification of this Ceratopogonid I owe to the kindness of Mr F. W. Edwards of the 
British Museum. 
2 Amman’s lactophenol, pure or mixed with 0-5 % of cotton-blue, which was used for the 
examination of the parasite, is highly recommended for similar purposes. 
