310 THE ZOOLOGIST. 
The first colouring matter which attracted much attention 
was that which is so widely distributed among plants—leaf- 
green or chlorophyll, as it is ordinarily called. You know that 
if a plant be kept in the dark its leaves lose their green colour, 
and you know also that when sunlight shines on green leaves 
under water little bubbles of gas continually rise to the surface ; 
this gas is oxygen, and it is known that chlorophyll is capable 
of breaking up carbonic acid in sunlight, storing the carbon and 
setting free the oxygen. 
In a few animals, the fresh-water sponge, the green Hydra, 
some Planarian worms, the protoplasm may be seen to contain 
chlorophyll-corpuscles ; and in the last of these Mr. Geddes 
has, by direct experiment, shown that in sunlight oxygen is 
given off, so that in them, as in green plants, the colouring 
matter is a producer of oxygen. The advantage of this to the 
animal is obvious; not only can it take in such oxygen as is 
dissolved in the water, but it can manufacture oxygen around of 
and for itself. That such an arrangement is desirable is, 
curiously enough, shown by another set of facts; in some of the 
Protozoa, the Radiolarians, and in the Sea Anemones naturalists 
have very frequently detected the presence of what they called 
‘yellow cells.” These were at first regarded as parts of the 
animal; but when it was found that they did not die when their 
host died, and that they could migrate from one individual to 
another, it was concluded that they were parasites ; and parasites, 
in a sense, they are. But, unlike such parasites as the tape-worm 
or the fluke, they give as well as take; their yellow colouring 
matter is capable of breaking up carbonic acid, and while these 
Alge—for such they are—store up for themselves the carbon, 
they set free the oxygen of which the host takes its share. 
This beneficial mode of clubbing together is now known as 
‘* Symbiosis.” 
In some of the marine Annelids (Sabella, Siphonostomum, 
Chloronema edwardsit) the blood is of a green colour; this 
colouring matter has been called by Lankester ‘‘ chlorocruorin,” 
and it presents in its oxidised condition an absorption-band 
between the lines C and D, and another, fainter, between D and 
EK; on reduction of the oxygen the spectrum has a single band 
which lies between C and D, but is somewhat fainter than the 
almost similarly-placed band of oxy-chlorocruorin. Just as 
