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MARINE ANIMALS 



hibited by the so-called telescopic eyes (Fig. 70). These are found 

 only in the smaller fishes, of which the largest, Gigantura chuni (Fig. 

 71), measures 11.8 cm. Such telescopic eyes have developed independ- 

 ently in five different orders and eight suborders of fishes. A deep-sea 

 cephalopod also has eyes of this type. 20 The similarity of the frontal 

 eyes of pelagic deep-sea crustaceans is only apparent, although there 

 is also a relative enlargement of the light-gathering surface. As a 

 further adaptation to the small amount of abyssal light, the retina of 

 the deep-sea fishes of all groups has only the light-sensitive rods; the 

 cones are absent. 21 



Nr- 





u— i 



\ -% 



Fig. 70. — Telescopic eye of the deep-sea fish Argyropelecus in transverse sec- 

 tion, with the dotted outline, U, of a normal eye for comparison. C, cornea; 

 L, lens; R, retina; Nr., pigmentary layer. After Brauer. 



In correlation with reduced eyes, and even with well-developed 

 eyes, in connection with this limited capacity for orientation in the dim 

 light, numerous deep-sea crustaceans and fishes possess antennae of 

 unusual length in comparison with those of their relatives in the lighted 

 zone. Sergestes magnijicus from 800 to 1200 m. has antennae three 

 times the length of the body; Arachnomysis, with well-developed eyes, 

 has antennae four times the length of the body; in the isopod, Mun- 

 nopsis longicornis (600-800 m. depth), the antennae are more than 

 eight times the body length, and in the shrimp Aristaeus they measure 

 10 to 12 times the length of the body. In numerous fishes, such as 

 Bathypterois (Fig. 72), single rays of the various fins are developed as 

 feelers and are longer than the body. A high development of the lateral 

 line system is also notable in many deep-sea fishes. Similar develop- 



