LIFE IN THE DEEP SEA. 585 



might have hoped to have met with animals of great antiquity in 

 the deepest holes, since these must possibly be regarded as 

 occupying the sites of very old depressions on the earth's 

 surface. 



Dr. Wallich, in his celebrated work, " The North Atlantic 

 Sea Bed/' unfortunately never completed,. though so full of most 

 important discussions of deep-sea phenomena, speaks almost 

 prophetically of the migrations of animals which "must take 

 place along the deep homothermal sea; that great highway, 

 extending from Pole to Pole,, which is for ever closed to human 

 gaze, but may nevertheless be penetrated by human intelligence."* 



Marine animals may throughout all time have migrated in 

 the course of generations across the equator, from north to south, 

 by way of the deep sea, and on reaching temperate or cold 

 latitudes, may have worked their way up into shallow water and 

 taken to coast life, and assumed forms more or less like those of 

 their ancestors who started on the journey. 



Eegarded as a high-road for migration across the equator, the 

 deep sea may well be compared with the summits of those moun- 

 tain chains which, in a similar manner, have acted as bridges 

 across the tropics for the passage of non-tropical plants. The 

 deep-sea animals themselves also, considered as a group, may be 

 well compared to Alpine floras, there being many points of 

 analogy between the two assemblages. 



As in the case of AJpine floras, plants which occur at sea- 

 level in cold or arctic regions, are found on high mountains in 

 temperate or tropical latitudes ; so in the case of the deep sea, 

 certain animals which in high northern or southern latitudes 

 exist in comparatively shallow water, occur at great depths near 

 the equator. Again, just as Alpine floras consist to a con- 

 siderable extent of modifications of forms growing at lower 

 levels in other regions of the earth, altered somewhat in non- 

 essentials to suit an Alpine existence, rather than of ancient and 

 isolated forms greatly differing from those of the lowlands ; so in 

 the case of the deep-sea fauna, hardly any of the animals dis- 



* G. C. Wallich, M.D., F.L.S., F.G.S., Surgeon-Major on the Eetired 

 List, H.M. Indian Army, " The Atlantic Sea Bed," Pt. 1, p. 105. London, 

 Van Voorst, 1862. 



