40 HIDDEN BEAUTIES OF NATURE 



the cilia may be seen in full activity. Cilia at all 

 times require high magnifying powers, but their 

 wave-like motions are well worth extra painstaking. 

 If tiny echini be taken when no larger than boot- 

 buttons, and carefully kept in seawater, they will 

 live for many months, and will always be available 

 for examination. No specimen is equal to the living 

 one for study. As regards the organs known as 

 pedicellariae, no true idea of their movements can be 

 realized except in the living specimens. Two friends 

 living at Dover kept young sea-urchins for a great 

 length of time. Repeatedly I have seen them under 

 the microscope, and on more than one occasion they 

 proved to be great sources of attraction at public 

 gatherings of the local Natural History Society. 



Again, when the specimens are dead, if we crush a 

 portion of one of the spikes into small fragments, 

 we shall see the transparent calcareous substance of 

 which it consists, and the secret of the remarkable 

 strength combined with lightness which characterizes 

 all spikes or spines of echinoderms. Each fragment 

 is joined to its fellow in a wonderful manner, and a 

 system of communications pervades not only the 

 spike but every portion of the solid parts of all 

 members of the sea-urchin group. This microscopic 

 structure of these marine organisms forms a most 

 fascinating branch of study to all who are at all 

 acquainted with it. The minute structure of the 

 shell is the same throughout, forming a sort of net- 

 work of carbonate of lime with a very small admix- 



