THE DYE OF THE DOG-WHELK. 297 



brated in ancient times, is also remarkable for 

 furnishing a permanent dye, which, although not 

 of the rich hue so highly prized in the classic 

 murex, makes nevertheless an indelible marking 

 ink of a purple colour. The colouring matter is 

 contained in a vein or gland in the animal's body, 

 easily found on breaking the shell. The fluid in 

 this receptacle is of a pale yellow tint, but such is 

 its chemical composition, that it is remarkably 

 affected by light. If it be applied when fresh to 

 white linen, and exposed to the sun, the pale tint 

 becomes a brilliant yellow: soon afterwards it 

 deepens into a delicate green, which grows darker 

 in its shade ; from green it gradually changes into 

 blue, then successively into indigo, red, and finally 

 purple. The relation which the rays of the sun 

 bear to colour, is a highly interesting subject of 

 study in chemical science, and probably a careful 

 analysis of the fluid now referred to might dis- 

 close some new relation which the sunlight bears 

 to certain substances, and might be of use in 

 suggesting some process in the arts. Independently 

 of any practical use, however, an investigation into 

 the causes leading to the vicissitudes of colour we 

 have just noticed, would be highly interesting in 

 a scientific point of view. 



The eggs of the Purpura, or dog-whelk, are 

 still more remarkable than those of the buccinum, 

 already described. They may be frequently dis- 

 covered on the recess of the tide adhering to the 

 surfaces of flat stones. These eggs are not 

 attached together in clusters, but placed separate 



