STAR-FISHES, SEA-URCHINS, ETC. 



747 



on a definitely symmetrical pattern with minute perforations, such perforations being most 

 distinctly visible on the inner surface of the shell. These minute punctures are the 

 apertures through which in life the delicate tubular locomotive organs, or so-called " feet," 

 are thrust out and retracted. The majority of these tubular organs terminate in a circular 

 sucking-disk, wherewith, collectively, the urchin is able to adhere to and travel over the 

 surface of the smoothest rock, or even up the glass walls of an aquarium. In the empty 

 beach-gathered urchin-shell a circular hole may be observed at the two opposite poles, the 

 one in the centre of the lower and natter surface being the larger of the two. It is within 

 this lower and larger one that the mouth, with its complex apparatus of teeth, is suspended. 





ILY 



fhate bj W Savilli-Ktnt, F.Z.S. 



LONG-SPINED SEA-URCHINS 



f nt in knrtk ACM of the* creature, may It sometime, seen on tidalJy e*po,ed 

 e neete-like spine, of * ~~rc ^^"^'^ Jere tK, poto g rap* <* 



excretory apertures. . f the structu ral details of the 



A noteworthy feature associated with the S^P five ; n the const ; tuen t 



sea-urchin which have been enumerated ,s the "^,1 ^rough which the tube-feet are 

 elements. It is found, for instance ..that the ^ rfo ated areas ^ 5ymmetri call y 



protruded form, as with the petals and othe nents y u!va i ent tooth -like structures, 



Corresponding segments, he dental apparcompr.es fiv ^q ^ ^ f 



characteristic of a,, the typ.ca, members 



