THE DISTRIBUTION OF ANIMALS 



449 



This abyssal fauna differs in many interesting features from 

 any other fauna. It is essentially carnivorous : the larger and 

 stronger fishes feed on the smaller and weaker; the latter feed 

 on the invertebrates ; the invertebrates feed on one another. 

 In addition much food comes to the deep-sea animals from the 

 death of the animals which make up the pelagic fauna. The 

 latter, on dying, sink rapidly; jellylike animals are said to sink 

 4000 meters in less than three days : on the other hand, decay 

 and disintegration are slow in deep water ; but eventually such 

 pelagic remains as are not devoured, disintegrate and, mingled 

 with the water, form a sort of organic slime or broth, which is 

 spread out in a thin layer over the oceanic basins, and doubtless 

 serves as food for the smaller and less active abyssal animals. 

 When first discovered it was believed to be a very primitive 

 organism ; it was preserved in alcohol, carefully studied under 

 the microscope, given the generic name Bathybins, and very 

 much theorized about. Later it was shown that what was called 

 Bathybius was merely a flocculent precipitate of calcium sul- 

 phate which the organic matter had thrown down from the sea 

 water in the presence of alcohol. 



We have already noted the looseness of structure of deep-sea 

 animals ; many fishes have skeletons largely cartilaginous in- 

 stead of bony, as in corresponding pelagic genera. Not a few 

 abyssal species are blind, but as a rule the eyes are as well 

 developed as in surface and littoral species, and are of use, as we 

 have already noted, in the pale phosphorescent light with which 

 many abyssal animals are endowed. Very many exhibit a bril- 

 liant coloration, possessing almost all the colors found in the 

 littoral fauna ; we can assign no use to such colors in the ab- 

 sence of sunlight at such great depths, but they afford a strong 

 argument for the theory that the abyssal fauna is derived from 

 the littoral fauna by a migration of the latter into deep water. 

 This migration was doubtless comparatively recent, geologically 

 speaking, for no palaeozoic animals have been found in the deep 

 sea ; on the other hand, there are more representatives of Meso- 

 zoic and Tertiary types than we find to-day in the littoral fauna, 

 and it is this which gives the abyssal fauna its peculiar facies. 

 We may now glance at some of the more characteristic deep- 

 sea types. 



2G 



