386 Proceedings of the Royal Society 
important of the colouring matters of sponges, while Merejkowsky * 
now finds it in fishes and in almost all classes of invertebrate 
animals. It has been strongly suspected to be an oxygen-carrying 
pigment, an idea to which these observations seem to me to give 
considerable support. It is, • moreover, readily bleached by light, 
another analogy to chlorophyll, t 
When one exposes an aquarium full of Anthea to sunlight, the 
creatures, hitherto almost motionless, begin to wave their arms, as 
if pleasantly stimulated by the oxygen which is being developed in 
their tissues. Specimens which I kept exposed to direct sunshine 
for days together in a shallow vessel placed on a white slab, soon 
acquired a dark unhealthy hue, as if being oxygenated too rapidly, 
although I protected them from any undue rise of temperature by 
keeping up a flow of cold water. So, too, I found that Radiolarians 
were killed by a day’s exposure to sunshine even in cool water, and 
it is to the need for escaping this too rapid oxidation that I ascribe 
their remarkable habit of leaving the surface and sinking into deep 
water early in the day. We may readily understand the mechanics 
of this phenomenon by remembering that the starch formed during 
the morning’s exposure to sunshine would increase the specific 
gravity of the Radiolarian, and so sink it, while its digestion and 
oxidation would again lighten it. 
It is easy, too, to obtain direct proof of this absorption of a great 
part of the evolved oxygen by the animal tissues through which it 
has to pass. The gas evolved by a green alga ( Ulva) in sunlight 
may contain as much as 70 per cent, of oxygen ; that evolved by 
brown algae ( Haliseris ), 45 per cent. ; that from diatoms about 42 
per cent. That, however, from the animals containing Philozoon , 
gave a much lower percentage of oxygen, e.g ., Velella , 24 per cent. ; 
white Gorgonia , 24 per cent.; Ceriaetis , 21 per cent.; while Anthea , 
which contains most algae, gave from 32 to 38 per cent. This 
difference between the amount of oxygen evolved by free and 
imprisoned algae is naturally to be accounted for by the avidity for 
oxygen of the animal protoplasm. 
* Comptes rendus, 1881. 
t Krukenberg, however, disputes the identity of Merejkowsky’s pigment 
with that which he has investigated, as well as the analogy of the former to 
haemoglobin. See his Vergleich. Physiol, d. Verdauung., Heidelb., 1882. 
