DEEP-SEA FAUNA. 



139 



found, indicating the changes that may have 

 taken place in the history of the blind Fish of 

 the abyss. In the genus of deep-sea Cods 

 (Macrurus) for example, those species which live 

 in water of less than a thousand fathoms depth 

 have very large eyes, and those that are found 

 in greater depths have much smaller ones. 



The same in general is true of the Crustaceans. 

 The deep-sea Cray-fish have lost not only their 

 eyes, but also the stalks which supported them. 

 In Bathynomus (a Crustacean belonging to the 

 group Isopoda\ however, there is a pair of 

 enormous eyes. 

 But as a rule 

 the eyes of 

 Crustaceans de- 

 generate and 

 disappear in 

 shallower water 

 than the eyes 

 of Fishes. At 

 depths of 500 

 f atho ms or 

 greater, the eyes of the Crustaceans usually show 

 signs of reduction in size or other retrogressive 

 changes, and in the greatest depths they are 

 nearly always wanting altogether. 



Accompanying the loss of eyesight in deep-sea 

 animals we often find a very remarkable de- 

 velopment of organs, which may be regarded as 

 especially tactile in function. 



Many of the deep-sea Fish, for example, with 

 rudimentary eyes possess long barbels, and in 

 some cases the paired fins are enormously 



FIG. 36. A deep-sea Fish showing very 

 elongated .fins 



