152 THE FAUNA OF THE DEEP SEA 



off or ruptured during their capture, but still the 

 horny rods that support them are shorter than they 

 are in shallow-water forms, and the general evidence 

 of their structure tends to show that they have 

 undergone profound modifications in the change to 

 the conditions of deep-sea life. 



An extremely common and almost general 

 character of deep-sea fishes is the black coloration 

 of some of the body cavities ; this is limited to the 

 pharynx in many of the fishes that live about the 

 hundred fathoms limit, but the colour is more intense 

 and spread all over the oral, branchial, and peritoneal 

 cavities in typical deep-sea forms. It may seem very 

 difficult at first to account for this remarkable de- 

 velopment of black pigment in parts of the body that 

 are not usually, and, in some cases, cannot at any 

 time be exposed to view. It is obvious that it can- 

 not be functional as a hiding colour, either in offence 

 or defence. But it is quite possible that it is due to 

 some modification of the function of excretion. It is 

 well known that in many cases of disease or injury to 

 the kidneys in vertebrates, the colour of the skin is 

 affected, and every one recognises now the fact that in 

 many invertebrates the colour of the skin is greatly de- 

 pendent upon the function of the secretion of the urates. 



