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the genus, and for reasons which it is partly the object of this 
Paper to give. 
Several Stylonichide, Phacus, and Ophrydium are invariably 
coloured green, and probably only await the examination 
suggested to be likewise added to the list. 
Sorsy has made a most careful examination of Spongilla ; 
- he found that the green colouring matter was not a simple one, 
but could be separated into a blue and a yellow colouring 
matter, in which he found several other substances, Xanthophyll 
principally. These were determined by their characteristic 
bands on spectroscopic examination, their solubility in alcohol 
ether, and castor oil; and their dichroism. 
This is precisely what we know the so-called Chlorophyll of 
plants to be. What, then, we may ask, is the function of this 
Chlorophyll, in animals ? 
In 1878 Geppss, working at Roscoff, found a marine plan- 
arian, green in colour, Convoluta Schultzii, which, on exposure to 
direct sunlight, gave off oxygen gas as much as 45 to 55 per 
cent. The green cells further contained starch in abundance. 
With these preliminary facts regarding the question, I now 
submit a few personal observations. 
In a lecture on the Huglenidae which I delivered to the 
Natural History Society at Stroud, some short time ago, the 
subject of which was the animal nature of those organisms, I 
suggested, knowing I had several ardent microscopists in my 
audience, that a search for pure gatherings of Euglena viridis 
should be made. If such could be found I pointed out the 
interest which would attach to a series of experiments similar 
to those made by Sorpy on Spongilla, and that, in addition, the 
action of sunlight on the animal and the determination of the 
gas or gases evolved should be carefully noted. This suggestion 
produced a speedier result than could have been expected. 
Very shortly after Mr W. H. Hortanp sent me a sample of a 
gathering of Euglena viridis, exceedingly rich in specimens, 
and asked me to say whether it was pure enough to satisfy us 
that any results it might give could fairly be attributed to that 
organism and none other. 
