D. Keilin 
99 
no stages of the multiplication of the parasite could be detected. To find the 
earlier stages of infection it was impossible to select the parasitised larvae 
with the naked eye. For this purpose each larva had to be examined separately 
under a high magnification, a very long and difficult task, because (1) the 
larvae are insufficiently transparent owing to their cuticle being lined with a 
layer of the fat body, whilst (2) the early stages of the parasites are minute 
and easily confused with droplets of fat or albuminoid corpuscles which often 
escape from the fat body of the slightly compressed larva. 
After selecting living larvae which I suspected to contain the early stages 
of the parasites, I proceeded to make smears of their bodies, which after 
fixation and staining, revealed, with very few exceptions, the early stages of 
this parasite. 
In this way I have collected a fairly rich material showing the various 
stages of the parasite. This material was studied in the form of smears as well 
as in sections of the larva. 
As to technique, I may state that all classical methods of Protozoology 
were used. I have obtained the best results from the smears fixed in Schaudinn’s 
fluid (with the addition of 1 per cent, acetic acid) and stained in iron-haema- 
toxylin and from sections of the larvae fixed in Carnoy’s fluid and stained 
also in iron-haematoxylin or in haemalum. 
II. The Life-history of Helicosporidium parasiticum. 
1. Localisation of the parasite. 
All the stages of the parasite are usually found free in the body cavity of 
the host. In several cases, however, especially when the infection was only 
recent, the parasites were found either in the fat body or in nerve ganglia. 
When they attack the fat body, the latter is rapidly destroyed and the 
parasites, attached to the fat droplets, escape into the body cavity. On the 
contrary when the nerve ganglia are infected, the infection remains for a 
long time localised; all the stages are then present simultaneously in the 
ganglia which become swollen and reduced to the neurilemma. It is interesting 
to remark that several successive nerve ganglia of the ventral chain may be 
infected, but the parasites are never found in the nerve commissures. 
2. Early stages and schizogony. 
The youngest stage of the parasite found in the tissue or in the body cavity 
of the host, is represented by small round corpuscles of 2 or 3p, in diameter 
(PI. IV, figs. 1, 2, 3); they are sometimes oval in shape, being then 3/z long and 
1-5/x wide. The protoplasm of these corpuscles is homogeneous, being devoid 
of granulations and vacuoles. The nucleus, in the form of a spherical chromatic 
granule 0*5p, in diameter is surrounded by a clear zone of protoplasm of 0-75/x 
in diameter. This clear zone may be the real nucleus, while the chromatic 
granule is the nucleolus—this, however, could not be proved, as it was im- 
7—2 
