84 PELAGIC FAUNA 



photographic lamp. Spirula inhabits all the great oceans, especially the mid- 

 waters from 200 metres downward, but is not found at the deepest levels. 

 At a station off Natal, between 500 and 600 metres deep, we took no 

 fewer than 26 specimens in a single haul. 



Most of the octopuses are bottom-dwellers, but a few have successfully 

 adapted themselves to a pelagic existence. The bodies of the pelagic forms 

 are soft with a weakly developed musculature, and most have a thin 

 membrane forming a web between the arms, often extending to the tips. 

 They swim bottom up in graceful, pulsating motions like a jellyfish, moving 

 their arms in and out. All are bathypelagic, though Alloposus, which we 

 found at several stations in the Indian Ocean, and which had previously 

 been known only from a few scattered localities in the warm regions of 

 all three oceans, seems to keep fairly close in-shore, spending perhaps 

 part of its time on the bottom. It has very large eyes and is translucent. 

 A genuine deep-sea cephalopod is Vampyroteuthis infernalis (Fig. p. 83), 

 which has been considered extremely rare. It is a velvety-black, broad- 

 webbed creature with a few light organs on the body and fins. Several 

 primitive features of its internal structure are regarded as evidence of its 

 belonging to a group of cephalopods otherwise extinct since the Creta- 

 ceous period. We found it in the Bay of Bengal, in the Java Deep, and 

 in the Kermadec Trench, always in very deep water. Off Durban, at a 

 depth of about 3,000 metres, we took a specimen 22 centimetres long, 

 twice the length of the longest hitherto recorded. 



The most fantastic forms are found among the deep-sea fishes. The 

 great majority of the really bathypelagic species are a uniform black, 

 blackish brown, or blackish violet, matt and lustreless. Some have scales 

 and some are without scales. The skeleton and musculature are more or 

 less degenerate, the fishes presenting a loose and flabby appearance. It 

 is popularly believed that animals accustomed to the massive pressure of 

 deep waters will burst if brought to the surface. This is true only of fishes 

 which have a closed swim-bladder, and real deep-sea fishes have no swim- 

 bladder. Some bathypelagic fishes are either blind or have very small eyes; 

 others have "telescopic" eyes, which are thought to increase their powers 

 of vision owing to the increased distance between lens and retina. Some 

 have light organs and some have not. Many have large jaws and long 

 teeth. 



A deep-sea fish which is not noticeably adapted is Bathytroctes; it has 

 a fairly normal fish shape, small teeth, and very large eyes, and in colour 

 is blackish brown with a violet head. The genus Opisthoproctus is re- 

 markable for its telescopic eyes in the shape of two parallel tubes, set like 



