THE EOMANCE OF NATURAL HISTORY. 



places within or near the tropics, where they are 

 needed. Professor Agassiz has shewn that it is 

 not difficult to obtain living specimens of the 

 zoophyte, and to preserve them, so as to study at 

 leisure their habits and motions. Why, then, it 

 has been asked, as we employ the silk- worm, and 

 furnish it with food and material to spin for us our 

 silks, and as we plant and form beds of oysters 

 in favourable locations, where we please, may we 

 not also employ the agency of the coral litho- 

 phyte, to lay the foundations, for instance, of a 

 lighthouse, or to form a breakwater where one is 

 needed? Such a practical result is by no means 

 improbable, from the minute and scientific obser- 

 vations now making upon these busy little build- 

 ers of the deep.* 



Let us look now at another class of labourers 

 by whom mighty deeds are performed, though the 

 performers themselves are so inconceivably minute, 

 that to say they bear the same relation to the 

 coral polype that a mouse does to an elephant, 

 would be greatly to overrate their dimensions. 

 They are, in fact, invisible to the sharpest sight, 

 except when aggregated together. I refer to the 

 Dintomncc;!'. 



Of late years the attention of microscopic ob- 

 servers has been largely and increasingly occupied 

 by a tribe of organic beings which are found to 

 exist in all parts of the world, in fresh and salt 

 waters chiefly, and present a great variety of 

 species as well as of form and markings. They 

 consist of a glassy shell, formed of flint, inclosing 

 a soft coloured substance, generally of a golden 

 yellow or brown hue. This is called the endo- 

 chrome, and the shell is called the frustule. The 

 latter has a determinate form, which often as- 

 * Cheever's " Sandwich Islands," Appx. p. 310. 

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