178 THE DISTRIBUTION OF 



with the latitude for the reasons already discussed, 

 there seems to be a fauna of silvery or iridescent 

 animals, of which the fish have been chiefly investi- 

 gated, though medusae, and doubtless other forms also 

 occur. The fish Uving at these depths inhabit an 

 environment where a considerable amount of sunhght 

 penetrates, especially blue and violet rays. They have 

 often large eyes, which sometimes protrude at the end 

 of short stalks, and are then called telescopic. Large 

 light organs are present, which perhaps catch the last 

 rays of sunlight. An example is the silvery fish Argyro- 

 pelecus affinis, which lives in the Atlantic at depths of 

 somewhere about 200 fathoms ; at night, when the 

 light conditions are the same near the surface as in the 

 depths where it habitually dwells, this fish has been 

 found -within some 80 fathoms of the surface. Its 

 young have the same colouring as their parents, and 

 live in the same depths. Another form with the same 

 colouring and characters is Cyclothone sig)iata, which 

 lives at a depth of about 300 fathoms. 



Still deeper, at depths of from 300 to 500 fathoms, 

 where all trace of red and green rays have completely 

 disappeared, occur forms in which the colouring is 

 black or red. In the absence of any red rays both 

 these colours must look the same, and either wiU pro- 

 tect the animal. At these depths occur deep-red or 

 chocolate-coloured medusae, the only pelagic echino- 

 derm (Pelagothuria), bright-red prawns, such as 

 Acanthephyra muUispina, and red or black fish, Se- 

 bastes norvegicus being an example of the former and 

 Gonioskma elongatum of the latter. The last-named 

 fish is purplish-black, with small light organs and 

 small eyes. It has huge jaws, a common feature in 

 these deep-water fish. A very curious point about it 



