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Helicosporidium parasiticum 
All this shows clearly that Helicosporidium parasiticumi, although a common 
parasite of Dasyhelea obscura , is by no means specific to this host, but occurs 
in other Dipterous larvae like Mycetobia pallipes and what is still more remark¬ 
able, in at least one other Arthropod, the Tyroglyphid mite Hericia hericia 
(Robin) Kramer, 1899. 
IV. Systematic Position of the Genus Helicosporidium . 
Now that we know the structure and the life-history of Helicosporidium , 
a question arises as to the systematic position of this genus. It seems to me 
very difficult to answer this question and all I can do at present is to discuss 
the relations between the new parasite and various forms of Protists. 
1. Helicosporidium and Cnidosporidia. 
One is tempted first of all to compare the genus Helicosporidium with the 
Sporozoa, especially those which have multicellular spores, as for instance 
Cnidosporidae, comprising the three Orders: Myxosporidia, Actinomyxidia and 
Microsporidia. 
The trophozoite stage of Helicosporidium as well as its schizogonic cycle 
recalls in many respects those of the Microsporidia Monosporogenea Perez 
(i e.g . Nosema bombycis); on the other hand, the trophic stage, in the form of a 
small round cell, as well as the schizogonic cycle, cannot be used for establishing 
the affinities between the various groups of Profcists as similar modes of 
multiplication can be found in widely separated orders. 
On the other hand the development and the structure of the spores 
provide a series of much more important characters which have been used 
already with success in the classification of the Protozoa. A character which 
is common to all Cnidosporidia and Helicosporidium is the complicated 
multicellular structure of the spores, the latter in both cases being composed 
of heterogeneous elements. It remains to be seen, however, in how far the 
spore cells of Helicosporidium can be compared with those of the Cnidosporidia. 
It may be assumed, for instance, that the three central cells or sporozoites 
of Helicosporidium correspond to the germ cells, sporoplasm or sporozoites of 
the Cnidosporidia, while the polar capsule of the latter corresponds to the 
spiral filament of our parasite. 
It must be admitted, however, that this assumption, which at first sight 
appears to be reasonable, is based on very superficial points of resemblance, 
and it needs a critical examination. The germ cells or sporoplasm of the 
Cnidosporidia differ from those of Helicosporidium in that they are usually 
reduced to a single binucleated cell, instead of three uninucleated cells as in 
Helicosporidium. 
Among the Cnidosporidia the uninucleated sporozoites are known in a few 
species of Actinomyxidia, but they are very numerous in each spore. 
As to the filament of Helicosporidium , although it is formed from one 
