456 



THE OCEAN WORLD. 



a very large shell, consisting of seven turns of the spire, studded with 

 spines, and terminating in a strong beak ; the other had a shell much 

 smaller. Aristotle named the last animal Buccinum. It is thought 

 that the last" species is to be recognised in the Purpura lapillus 

 (Fig. 285), which abounds in the Channel. Reaumur and Duhamel 

 obtained, in fact, a purple colour from this species, which they applied 

 to some stuffs, and found that it resisted the strongest lye. The 

 genus Murex is supposed by some to have contained the species 

 indicated by Aristotle. 



Up to the present time, the production of the Tyrian purple remains 



Fig. 284. Cassis zebra (Lamarck). Fig. 285. Purpura lapillus. Fig. 286. Purpura patula. 



a mystery. It was long thought this fine dye was furnished by the 

 stomach and liver ; but M. Lacaze-Duthiers has demonstrated 

 that the organ which secretes it is found on the lower surface 

 of the mantle, between the intestines and the respiratory organs, 

 where it forms a sort of fascia, or small band. The colouring matter, 

 as it is extracted from the animal, is yellowish ; exposed to the light, 

 it becomes golden yellow, then green, taking finally a fine violet tint. 

 While these transformations are in progress a peculiarly pungent 

 odour is disengaged, which strongly reminds one of that of assafcetida. 

 That portion of the matter which has not passed into the violet tint 

 is soluble in water ; when it has taken that tint it becomes insoluble. 

 The appearance of the colour seems provoked rather by the in- 

 fluence of the sun's rays than by the action of the air, The matter 



