756 GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 



Littoral zone, exposed at low tide, with its acorn shells and 

 periwinkles, limpets and cockles, to the Laminarian zone 

 (to 15 fathoms) with its sea slugs and oysters, where the 

 great seaweeds wave listlessly amid an extraordinary keen 

 battle, to the Coralline zone (15-40 fathoms), with its carni- 

 vorous buckles, what variety and abundance, what crowd- 

 ing 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 on the rocks and sandhoppers among the 

 jetsam, a few insects about high-tide mark, sea-spiders 

 clambering on the seaweeds, abundant bivalves and gastero- 

 pods, sea-squirts in their degeneracy, besides fishes, a few 

 reptiles, numerous shore birds, and an occasional mammal. 

 The shore fauna is thus very representative, rivaUing in its 

 range that of the open sea, far exceeding that of the abysses. 



The conditions of life on the shore are in some ways the 

 most stimulating in the world. It is the meeting place of 

 air, water, and land. Vicissitudes are not exceptional, but 

 normal. Ebb and flow of tides, fresh-water floods and desic- 

 cation under a hot sun, the alternation of day and night felt 

 much more markedly than on the open sea, the endless 

 variations between gently lapping waves and blasting 

 breakers, the slow changes of subsidence or elevation, — 

 these are some of the vicissitudes to which shore animals 

 are exposed. The shore is rich in illustrations of keen 

 struggle for existence and of life-saving shifts or adaptations, 

 such as masking, protective coloration, surrender of parts, 

 and " death feigning." We may think of it as a great school 

 where many of the great lessons of life, such as nioving head 

 foremost, were learned. 



The Fresh Water Fauna. 



Perhaps the most striking fact in regard to the animals 

 which live in fresh water is their uniformity. The number 

 of individuals in a lake is often immense, but the number 

 of species is relatively small, the number of types still 

 smaller. In widely separated basins and in diff"erent 

 countries the same forms occur. 



