930 LIVERPOOL BIOLOGICAL SOCIETY. 
considerable depths, pink or red (Bowerbank).”’ I had 
excellent opportunity of convincing myself of this varia- 
tion in colour in one of the large caves at Puffin Island, in 
April, 1889. The cave, situated on the north end of the 
island, is accessible only at lowest spring tides, and even 
then only with boat. Right at the entrance to the cave 
I noticed that the specimens of Pachymatisma were of a 
dark slate-grey colour. Rowing further into the interior 
I found specimens of a light grey, and in the farthest recess 
of the cave I discovered some splendid specimens of a 
perfect cream-white tint. I found quite similar conditions 
in April, 1890, near Brada Head, Port Erin, in a cave 
which also is accessible only with boat and at lowest tide. 
The specimens of Pachymatisma, larger even than those at 
Puffin Island, were lighter in colour the further back in 
the cave they were found. 
The explanation of these facts is, in my opinion, found 
only in the direct action of the hight of the sun. The 
more exposed the specimens were to the light, the darker 
they were; the more protected, the lighter. I know very 
well that such an explanation is not at all in accordance 
with the generally accepted views, and Wallace’s* state- 
ment, “‘ that light and heat of the sun are not the direct 
causes of the colour of animals,” is not only his own 
view, but is shared by the majority of modern biologists, 
Still my own view finds support in what Lendenfeld + 
has recently said in regard to the Ceratosa—‘“‘ No differences 
are observed in the colour of different parts of the surface 
except that the lower side is generally lighter-coloured 
than the upper side. This is less of a protective acquisi- 
tion than a direct effect of the light. The parts of the 
surface exposed to it are darker coloured by its photo- 
* Wallace, ‘‘ Darwinism,” p. 195. 
+ R. v. Lendenfeld, ‘A Monograph of the Horny Sponges,” p. 742. 
