THE AMCEBA, HYDRA, AND OTHER SIMPLE ANIMALS 121 



many being of the most exquisite symmetry and beauty. 

 Tliey are perforated by many small holes through whicli 

 project long, delicate, protoplasmic pseudopodia. These 

 fine pseudopodia often interlace and fuse when they touch 

 each other, thus forming a sort of protoplasmic network 

 outside of the shell. In some cases there is a complete 

 layer of protoplasm — part of the body protoplasm of the 

 Protozoan — surrounding the cell externally. 



Fig. 84. — Rosalina vnriaiis, a marine protozoan (Foraminifera) with cal- 

 careous shell. (Greatly magnified; after Schultze.) 



VVhen these tiny animals die their hard shells sink to 

 the bottom of the ocean, and accumulate slowly, in incon- 

 ceivable numbers, until they form a thick bed on its floor. 

 Large areas of the bottom of the Atlantic Ocean are cov- 

 ered with these beds. Nor is it only in present times 

 that such beds have been formed by the marine Protozoa. 

 All over the world there are thick rock strata composed 

 almost exclusively of the fossil shells of these simple 

 animals. The chalk-beds and cliffs of England and of 

 France, Greece, Spain, and America, were made by 

 marine Protozoa. Where now is land were once oceans, 



