1913] on Reflection in Aquatic and Sub-Aquatic Life 7^5 



In conclusion, I will refer to reflection as a revealing factor. I 

 have already illustrated this point with the anemone. I now show 

 a slide of a shoal of young rudd wheeling round, and as they turn 

 each fish is revealed as a flash of light as he catches the light from 

 above. 



Among diving birds the cormorant does not retain air bubbles in 

 his feathers to the same extent as the loose-plumaged water-hen, yet 

 by reflection he appears light or dark, according to the nature of the 

 bottom over which he is swimming. When, however, the cormorant 

 dives bis track is marked by a series of brilliant flashes of light. 



Now this bird when swimming on the surface has the habit of ' 

 dropping his head under water at regular intervals — shags do the 

 same. Seen from below, every time he does this, there is a flash of 

 light not unlike the flash from a silvery fish turning. It is quite 

 possible that fish, such as pollock and codling, are attracted by this 

 flash, and thus swim towards their destroyer. 



These flashes of light are still better shown in the case of the 

 penguin, and this I illustrate with individual pictures cut out of a 

 cinematograph film. 



I have had to leave the subject of refraction of light on the 

 present occasion ; firstly, because time does not permit of my 

 dealing with it, and secondly, because during the last fortnight I 

 have tested all my experiments at Port Erin, and some of the results 

 have made me reconsider the conclusions at which I had arrived with 

 regard to the refraction of light in its relation to marine organisms. 



[F. W.] 



