148 THE FAUNA OF THE DEEP SEA 



CHAPTER VIII 



THE FISH OF THE DEEP SEA 



OF all the groups of animals that constitute the 

 deep-sea fauna, the fish show the greatest number 

 of peculiarly abysmal characters. Being much 

 more highly differentiated than the invertebrates, 

 they possess more organs liable to undergo modi- 

 fications of colour, size, and structure, and conse- 

 quently we are able to point to a great many more 

 features characteristic of deep-sea fish than we can 

 do in any other group of animals. 



The first point that calls for remark in the con- 

 sideration of the fish fauna of the deep sea is the 

 almost entire absence of ancient and primitive types. 

 The Elasmobranchii, including the Sharks, Kays, and 

 Chiinsera, constituting the order that from anatomical 

 embryological grounds is always regarded by natura- 

 lists as the most primitive order of this class, is 

 represented in very deep water by only one species. 



