156 ANIMAL LIFE OF THE DEEP SEA BOTTOM 



chain; namely, crustaceans, which eat the worms and in turn are eaten 

 by fishes. 



Dr. T. Mortensen, one of the Galathea Expedition's loyal and most 

 interested supporters, was surprised during his world voyage as long ago 

 as in 19 14 — 16, and again in Indonesia in 1922, to find large numbers 

 of sea-urchins and other animals in deep water where there was an abun- 

 dance of dead vegetation, and to find also that there were vegetable re- 

 mains in the stomachs of some of the sea-urchins. Deep-sea sea-urchins 

 are unlikely to be vegetarians, but must have found in the vegetable 

 remains such an abundance of bacteria, protozoa, worms, and the like 

 that if only they went on eating there would be sufficient digestible ani- 

 mal matter to sustain them. 



But there is a further source of food supplies from above, which can 

 almost be described by saying that some species bring their food with 

 them from the surface layers. This applies, in fact, to a large proportion 

 of all the fauna of the psychrospheric water; namely, all the species 

 which breed in the surface layers. It includes both bathypelagic animals 

 and forms which live high up on the continental slope or down in the 

 abyssal zone. 



We will take as an example a genus of deep-sea eels (Synaphobranchus), 

 which in various species is distributed over the bottom of all the oceans 

 down to about 3,500 metres. The Danish Ingolf Expedition took it off 

 West Greenland, and many other expeditions, including the Galathea, 

 have caught it all o\'er tropical and subtropical regions, though never 

 in the Mediterranean, which the cold water masses of the Atlantic are 

 prevented from entering by the sill of the Straits of Gibraltar. 



It is with these deep-sea eels as with our fresh-water eel: when ready 

 to spawn they make for the warm thermospheric water. There and only 

 there do we find the characteristic larvae of these and all other eels, the 

 so-called Leptocephali. Our European eels, as my teacher Johannes 

 Schmidt found on his expedition years ago, migrate to the Sargasso Sea, 

 north-east of the West Indies, and there we find their larvae along with 

 those of other eels, including the North Atlantic deep-sea eel. The larvae 

 live in the rich surface levels until their metamorphosis to elvers; then 

 only do they migrate to the adult habitat, either fresh water or the cold 

 deep-sea bottom as the case may be. 



Here we must say a few words about the at times overwhelming 

 lavishness of Nature with individual lives in order to maintain the whole 

 — • in this case the species — generation after generation. First our own 

 eel: countless myriads swarm over to our shores every spring, pushing up 



