30 THE SEA-SIDE AND AQUARIUM. 



surfaces of uniform colour; for, from the admixture 

 of mucous with the colouring matter, when any 

 quantity of the latter is collected, the hue is found 

 to imbue the cloth in a mottled or blotched manner, 

 some parts being much darker than others. What 

 method the ancients had of avoiding this appearance, 

 I do not know." 



But we must not conclude this chapter without 

 noticing a curious property possessed by this mollusc. 

 This is its extraordinary voracity, a property noticed 

 by old writers like Pliny, and confirmed by Cuvier, 

 and other modern writers. Mr Sowerby thus de- 

 scribes its mode of piercing : 



"Gliding stealthily among the sea-weeds and stones, 

 it" (fhePurpura) "seeks its prey, and woe to the small 

 Winkle, Limpet, or Trocluit, that comes within reach 

 of its terrible proboscis. It will bring the aperture of 

 its own shell opposite to that of its victim, and then, 

 introducing his apparatus, never leaves it until all the 

 soft parts are transferred to his capacious stomach. 

 But even where no aperture or door leaves the smaller 

 mollusc open to the attack of his enemy in that way, 

 he is by no means deterred by this little difficulty ; 

 for if the object of his attack be a Limpet, firmly at- 

 tached to a stone, or a Bivalve tenaciously holding its 

 shell closed, he will manage to perforate the shell, 

 and through the hole draw the quivering substance. 

 Mr Spence Bates related to the authors of the ' British 

 Mollusca,' that by way of experiment he placed a 

 P'tirpura in a vessel of sea water, in company with a 



