The Mighty Deep 



differing from the warmth -loving foraminifera. 

 Sometimes immense floating banks of these 

 microscopic plants are found, reaching through 

 many miles. A net, lowered into such a bank 

 and then drawn up, is filled with a ''brown- 

 coloured slimy and felt-like mass," made up 

 chiefly of uncountable myriads of diatoms. 



Such masses are held together by a kind of 

 sticky jelly, and if the hand is passed through 

 it a very slight roughness may be perceptible, 

 caused by the flinty diatom shells or cases. 



Mere specks indeed they are, individually too 

 minute to be seen by a human eye, unaided. Yet 

 how marvellous in their make ! 



A Diatom plant or vegetable or sea-weed, 

 whichever we choose to call it, is like a For- 

 aminifer of the simplest possible structure. It 

 consists of a single cell, with an outside flinty 

 coatinCT or inclosure, answerino^ to the wood of 

 a tree or the skeleton of an animal. 



This flint casing, though infinitely small and 

 delicate, is yet firm enough to prevent the passage 

 of water through it ; and also it is practically 

 indestructible by ordinary forces. Diatom-cases, 

 dropping to the ocean-bed, may lie there for 

 ages. 



The living cell is inclosed in the said " case," 

 154 



