THE DIATOMACE^E. 99 



numerous apertures to admit the surrounding water into the 

 internal cell. Many species are always met with entirely free, 

 after the process of duplicative subdivision has once been com- 

 pleted; others remain adherent, forming stripes or bands or 

 spirals, or even plant-like structures of exquisite delicacy and 

 beauty, such as the Licmophora, or Fan-bearer, which is very 

 common .in April and May on the leaves of Algae, and is very 

 generally distributed round the British coasts, forming gela- 

 tinous masses of a clear brown colour on the plants it frequents. 



The Diatomacea? are found in fresh water streams and pools, 

 but they chiefly abound in the ocean, no part of which is with- 

 out its share of this ever-springing vegetation. Within the 

 Atlantic circle, Dr. Hooker found them washed up in myriads by 

 the sea on to the f pack and bergs,' everywhere staining the ice 

 and snow of a pale ochreous brown. Floating masses of ice when 

 melted yielded them in countless millions, and the sounding- 

 lead constantly brought them up from depths that would have 

 engulphed Chimborazo. 



The guano of the Chincha Islands contains innumerable 

 shells of Diatomacese, which the birds, through whose intestinal 

 canals they must have passed, drew forth with their prey out 

 of the abounding water ; and they are found in the dust which, 

 wafted from the Sahara by the hot breath of the desert, fre- 

 quently falls upon the decks of ships 300 miles from the African 

 coast. 



The indestructible nature of their flinty coverings has also 

 served to perpetuate them from time immemorial. Man and 

 all the higher animals pass away, and scarcely a vestige of their 

 existence remains, but the Diatomacese build for eternity. 

 Without cessation their remains are deposited upon the bottom 

 of the sea ; without cessation they are raising submarine banks, 

 and filling up estuaries and channels. At first sight it may seem 

 a gross exaggeration to attribute so vast an agency to beings 

 so minute, but when we recollect how quickly they multiply by 

 division, and how their activity dates from the first dawn of 

 organic creation, their architectural powers no longer seem in- 

 credible. In forty-eight hours a single Diatomacea is able to 

 multiply to eight millions, and in four days to one hundred and 

 forty billions, when the silicious coverings of its enormous pro- 

 geny would already suffice to fill up a space of two cubic feet ; 



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