48 H. C. SORBY. 
contain very closely allied substances, but I do not yet know 
any certainly identical. At all events, when looked upon 
from a chromatological point of view, such sponges are closely 
related to animals, or to those plants which, like them, are 
nourished by complex chemical compounds, and cannot be 
supported by merely mineral substances, like the more per- 
fect plants. 
In my paper on comparative vegetable chromatology! I 
have shown that the highest classes of plants contain the 
following essential constituents, soluble in carbon bi- 
sulphide : 
Blue chlorophyll. 
Yellow chlorophyll. 
Orange xanthophyll. 
Xanthophyll. 
Yellow xanthophyll. 
Lichnoxanthine. 
The constituents soluble in water are— 
Various kinds of chrysophyll. 
Various kinds of erythrophyll, which are often absent, 
and are not essential. 
Now, when I came to examine the fresh specimens of 
Spongilla fluviatilis I soon found that it contained all the 
above-named substances soluble in carbon bisulphide, and a 
small quantity of a yellow substance soluble in water, very 
similar to, if not identical with, one met with in many fungi, 
differing from the chrysophyli of the higher plants in not being 
made deeper coloured by alkalies or paler by acids. The 
other constituents appear to be absolutely identical with those 
in plants, and I cannot agree with Mr. Ray Lankester in 
looking upon the chlorophyll as a distinct substance.” 
There being thus very little qualitative difference between 
the Spongilla and the highest classes of plants, it became 
necessary to ascertain whether there was any well-marked 
quantitative difference, which would point to a closer relation 
to one class than to another. ‘The plan of analysis adopted 
was to separate the various coloured constituents, wherever 
possible, and to determine their relative amounts by mea- 
suring in long test tubes of equal diameter the lengths of the 
columns of liquid giving the same intensity of absorption 
with equal illumination, and, when the constituents could 
not be separated, to compare the respective absorption-bands 
in the same manner. I may here say that, unlike what 
1 * Proceed. Roy. Soc.,’ 1873, vol. xxi, p. 442. 
? See his paper in the ‘Journal of Anatomy and Physiology,’ vol. iv, p. 
119. 
