214 OYSTERS, AND ALL ABOUT THEM. 



blood is not much smaller. Those of a frog are twice as 

 large as one of these creatures. As the polishing slate has 

 no cavities, these animalcules lie closely compressed. A 

 cubic inch would contain, on an average, about forty-one 

 thousand millions of these animals. Of the forty-one 

 thousand millions of them, one hundred and eighty seven 

 millions go to a grain. A single shield of the Gaillonella 

 weighs about one hundred-and-eighty-seven-millionth part 

 of a grain. 



An ingenious device has been adopted by a modern 

 writer to cast light on immense numbers, of which it is 

 ordinarily so difficult to conceive. He says, if a million of 

 peas were placed on the floor of a room, it would require 

 to be sixteen feet square. Accordingly, it would require 

 one hundred and eighty-seven rooms, proportionately 

 smaller, to contain the animalcules that would amount in 

 weight to a single grain ! 



Ehrenberg calculated ihe fecundity or capacity of 

 microscopic animals to be so great that one of these 

 imperceptible animals can become, in four days, 170 

 billions, by germination or voluntary division. Many 

 strata in the earth are formed entirely of the remains of 

 infusoria, and a very familiar example is the Tripoli- 

 powder, from the polishing slate of Bilin, in Bohemia. A 

 single grain of Tripoli-powder contains no fewer than 

 187,000,000 of the transparent flinty skeletons of dead 

 animalculae ; yet the layers of the earth which are made up 

 of them extend for miles. In the harbour of Wisenar, in 

 the Baltic, they increase and multiply at a great rate, for 

 17,496 cubic feet of mud are formed there every year, and 

 every grain of it contains 100,000,000 of the beautiful 

 silicious remains of the infusoria. In the island of Barba- 

 does there is a thick mass of the most beautiful flinty sea 



