324 EVENINGS AT THE MICROSCOPE. 



Edward Forbes calculates that upon a large Echinus, 

 such as this dried specimen of E. s;phcera, there are 

 more than four thousand spines, every one of which 

 has the structure, the mechanism, and the movements 

 that we have been examining. Well may he say, that 

 " truly the skill of the Great Architect of Nature is 

 not less displayed in the construction of a Sea-m'chin 

 than in the building up of a world ! " 



To return now to our little E. miliaris, which has 

 been all this time coursing round and round his saucer, 

 wondering, perchance, at the narrowness and shallow- 

 ness of the White Sea in which he finds himself. Again 

 we peer, lens to eye, over the bristling surface, and dis- 

 cern, shooting up amidst the spines, and almost as 

 thickly crowded as they, multitudes of the tiny organs 

 which have caitsed so much doubt and discussion 

 among naturalists. Mliller, the great marine zoologist 

 of Denmark, who first discovered them, thought them 

 parasitic animals, living piratically upon the unwilling 

 Urchin, and accordingly gave them generic and specific 

 names. The term Pedioellaria, which he assigned to 

 his supposed genus, is that by which modern naturalists 

 have agreed to call them still, though the word is not ' 

 now used in a generic sense, since it is indubitably 

 established that they are not independent animals, but 

 essential parts of the Urchin itself. Miiller described 

 three distinct sorts, and I have added a fourth to the 

 number ; they are named P. trvpJiylla, tridens, gldbi- 

 fera, and stereophylla. They all agree in these particu- 

 lars : — that each has a long, slender, cylindrical, 

 fleshy stem, through the centre of which runs an axis 

 or rod of calcareous substance ; that the base of the 

 stem rests on the skin of the Urchin ; that on the sum- 



