208 FUNCTIONS AND INSTINCTS. 



cular fibres were distinctly visible, enveloping 

 the base of the spine, when the sac was removed ; 

 so that, reasoning from analogy, it may be con- 

 cluded that the spines of the common species 

 have a similar muscular apparatus. 



The spines vary much in their form and 

 sculpture. In the species last named they 

 seem to be of a horny substance, varying in 

 magnitude arid length, the larger ones tapering 

 from the base and being blunt at the tip, they 

 are beautifully fluted like the shaft of a co- 

 rinthian pillar. 1 The part enveloped by the 

 membrane before mentioned, is thicker than the 

 rest of the shaft, perfectly smooth, but terminates 

 in a bead : they are tinted with violet, but the 

 base and tip, or the pedestal and capital of the 

 pillar are white. The base is concave so as to 

 play upon the levigated centre of the above 

 protuberance. Besides these larger spines, there 

 are some bristle-shaped ones terminating in a 

 subovate knob, which when unfolded appears 

 to resemble a tripetalous flower with acuminated 

 petals, and which are supposed to be polypes. 2 

 Those parts void of spines, called the alleys, 

 distinguished by rows of orifices disposed in 

 pairs, are furnished with a quite different kind 

 of organ, I mean the suckers 3 before alluded to 

 and described, by which the animal can also move 



1 Echinus edulis, PLATE III. FIG. 14. 



2 Pedicellaria>, Ibid. FIG. 12, 13. * Ibid.Fio. 5. 



