CLASS PISCES 



363 



and continue to grow as long as they live. The rate of growth, however, 

 gradually diminishes as they get to an advanced age. 



389. Deep-sea Fishes. — There are many fishes which have become 

 adjusted to the conditions of life at great depths in the ocean and have 

 become highly modified in several directions (Fig. 256). Some of these 

 have become exceedingly slender, thus reducing the bulk of the body. 



Fig. 256. — Deep-sea fishes. A, Photostomias guernei Collett; length Ij^^ inches, taken 

 at a depth of 3500 feet. B, Idiacanthus ferox Giinther; 8 inches, 16,500 feet. C, Gastro- 

 stomus bairdii Gill and Ryder; 18 inches, 2300 to 8800 feet. D, Cryptopsaras couesii Gill; 

 2j^ inches, 10,000 feet. {From Lull, "Organic Evolution," after Schuchert, "Historical 

 Geology," by the courtesy of The Macmillan Company.) 



Another modification which is very general in these forms is the develop- 

 ment of enormous mouths, as if to make the most of the opportunities 

 presented for the securing of food. Sometimes the eyes are enlarged to 

 gather all the light possible, though in other cases they are small and 

 apparently useless. Luminescent organs are frequently developed. 

 Extraordinary shapes are assumed, and in one very marked type the 

 male has become minute, lives parasitically attached to the surface 

 of the female, and receives food passed from the blood vessels of the 

 female into its own, the two sets of vessels being in contact. 



