796 GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 



(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. 



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. But whensoever 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. 



Littoral. --At a very early date the shores were peopled, 

 and the fauna is very rich and representative. From the 

 strictly Littoral zone, exposed at low tide, with its acorn- 

 shells and periwinkles, limpets and cockles, to the Lam- 

 inarian zone (to 15 fathoms), with its sea-slugs and 

 oysters, where the great sea- weeds wave listlessly amid an 

 extremely keen battle, to the Coralline zone (15-40 fathoms), 

 with its carnivorous buckies, what variety and abundance, 

 what crowding and struggle ! 



There are Infusorians and Foraminifera, Sponges horny, 

 flinty, and limy, zoophytes and sea-anemones, a mob of 

 "worms," star-fishes and sea-urchins, crabs and shrimps, 

 acorn-shells onthe rocks and sandhoppers among the jetsam, 

 a few insects about high-tide mark, sea-spiders clambering on 



