PURPURA. 275 



The Purpura of the Komans, from which they pro- 

 cured their famous colour, was Murex trunculus, a com- 

 mon Mediterranean shell ; it is the principal subject of 

 Colonna^s essay. ' A similar dye is yielded by the two 

 European species of the present genus. It is secreted 

 by an organ which Lacaze-Duthiers considers a kidney, 

 urea having been detected in the liquid by chemical 

 analysis. I shall have occasion to say more about this 

 when I treat of P. lapilhis. Another point of resem- 

 blance, common to the ancient and modern Purpurce, is 

 their power of drilling holes in the shells of other mol- 

 lusca, for the purpose of feeding on them. The mussel 

 is especially the prey of P. lapilhis. A living naturalist 

 was mistaken in supposing that it invariably chooses 

 that part of the mussel- shell from which the epidermis 

 had been previously removed — as if the latter could be 

 any impediment to its operations. The late Mr. Osier 

 imagined that " the perforation is effected by a succes- 

 sion of strokes, following each other at intervals shorter 

 than a second : ^^ perhaps he was thinking of a wood- 

 pecker. Neither is the discovery of the perforating- 

 faculty possessed by whelks a new one as is generally 

 believed. It was mentioned more than twenty-two 

 centuries ago, by Aristotle, in the 4th chapter of the 4th 

 book of his wonderful '^ History of Animals.^ He there 

 describes the stout proboscis of the Tropcpvpa (which he 

 compares to that of the gadfly) and its use, as well as 

 its sharp minute and slender teeth, like those of snails. 

 Nor was he ignorant of its acute sense of smell, evi- 

 denced by the Tropcpvpa being attracted from a consider- 

 able distance by the bait laid for its capture. He like- 

 wise noticed the honeycomb-mass of spawn deposited by 

 that shell-hsh ; and all his observations are marked by 

 a degree of accuracy which scientific men now- a- days 



