THE LITTORAL FAUNA. 755 



pressure is enormous, thus at 2500 fathoms it is about 2\ 

 tons per square inch ; the cold water in sinking brings down 

 much oxygen ; it is quite calm, for even the greatest storms 

 are relatively shallow in their influence ; there are no plants 

 (except perhaps the resting phases of some Algae), for 

 typical vegetable life depends upon light, and not even 

 Bacteria, otherwise almost omnipresent, are known to 

 flourish in the great depths. A strange, silent, cold, dark, 

 plantless world ! The animals feed upon one another and 

 upon the debris which sinks from above, including the rain 

 of pelagic Protozoa, whose continual dying seems rather to 

 contradict Weismann's doctrine of their immortality. 



We do not clearly know when the colonising of the depths began, 

 but there is much to be said for the view that an abyssal fauna was, at 

 most, scanty before Cretaceous ages. One of the arguments is as 

 follows : In ancient days, when warmth-loving plants flourished in the 

 far north, when there was no ice-bound polar sea, the abyssal water 

 cannot have been so cold as it is now, it would therefore contain less 

 abundant oxygen, and this scantiness would make life more difficult. 

 But whenever the peopling of the abysses occurred, it must have been 

 gradual. It is likely that most of the pioneers migrated outwards and 

 downwards from the shore region (in a wide sense), following the drift 

 of food ; it is possible that others, e.g., some Crustaceans, sank from the 

 surface of the open sea. The boreal character of many deep-sea animals 

 has been often remarked, and it is plausible to suppose that there was a 

 particularly abundant colonisation in the Polar regions, and a gradual 

 spreading towards the Equator as the Poles became colder. Perhaps 

 the richness of the fauna at the Equator may be thought of as in part 

 due to the meeting of two great waves of life from the Poles. 



The abyssal conditions of life tend to uniformity over 

 vast areas, just as in the open sea. But, on the whole, life 

 must always have been harder in the depths than on the 

 surface. The absence of plants, for instance, involves a 

 keener struggle for existence among animals. Thus, 

 although many abyssal forms, e.g., sea anemones, live a 

 passive sedentary life, waiting for food to drop into their 

 mouths, the majority are less easy-going. The deep-sea 

 has been a sterner school of life than the surface. 



The Littoral Fauna. 



At a very early date the shores were peopled, and the 

 fauna is very rich and representative. From the strictly 



