RADIARIES. 207 



Yet as the spines are employed by the sea- 

 urchin to effect its motions, there must be some 

 intermediate agent, hitherto undiscovered, which 

 it has at its command, by which it can act upon 

 them. Dr. Cams' remarks on the zoophytes in 

 general are very applicable in the present in- 

 stance " When we find," says he, " that there 

 can be respiration without lungs ; that nutrition, 

 growth, and secretion may exist without a circu- 

 lation of fluids ; and that generation may take 

 place without distinct sexes, &c. why should 

 we doubt that sensitive life may exist without 

 nerves, or motion without muscular fibres ?" It is 

 important to be observed here, that these spines, 

 however strongly attached they may appear in 

 the living animal, in the dead one fall off upon 

 the slightest touch, which proves that the cause 

 of their adhesion is connected with its life. 



But though it is difficult to detect the muscu- 

 lar fibres that move the spines of the common 

 sea-urchin, I had an opportunity when correcting 

 the proof containing the preceding paragraph, 

 through the kindness of my friend Mr. Owen, 

 of the Hunterian Museum, well known for his 

 admirable anatomical description of the animal 

 of the pearly Nautilus, 1 of examining a prepa- 

 ration of the large spines, with their sacs, of 

 the mammillary Sea-urchin, 2 in which the mus- 



1 Nautilus Pompilius. 



2 Cidaris mamillatus, PLATE III. FIG. 4. 

 VOL. i. 08 



