176 ' JULY. 



furrows, visible only with a considerable magnifying 

 power, like the rounded masses of coral from the tro- 

 pical seas, called brain- stones. 



On the under surface similar stout short spines are 

 arranged in transverse bands across each ray, interrupted, 

 however, by the central furrow, which is perforated with 

 two ranges of orifices to give issue to the sucker- feet, 

 which thus form a double row. These organs do not 

 differ importantly either in structure, function, or ap- 

 pearance, from those in the Cross-fishes, in the Sea- 

 cucumbers, or in the Urchins. 



In health and activity the whole upper surface is 

 covered with a forest of short pellucid tubes, closed at 

 the tips, which protrude from pores in the plates, and 

 stand erect, moving, however, to and fro at the will of 

 the animal; they are evidently filled with fluid. I 

 cannot find any notice of these organs : they are pro- 

 bably connected with respiration. 



What a wonderful piece of mechanism is a Sea- 

 Urchin ! Accustomed as I am to the multitudinous 

 contrivances and compensations that present themselves 

 at every turn to the philosophic naturalist, often as sur- 

 prising and unexpected as they are beautifully effective, 

 I am yet struck with admiration at the structure of an 

 Echinus whenever I examine it anew. A globular 

 hollow box has to be made, of some three inches in 



