230 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. Eight at the entrance to the cave 

 I noticed that the specimens of Pachymathmd were of a 

 dark slate-grey colour. Kowing 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 light 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 Lendenfeldf 

 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. 



t R. V. Leiidenfeld, "A Monograph of the Horny Sponges," p. 742. 



