THE SEA SNAIL 25 



a few minutes 1 time it would have turned to yellow. 

 After a little time longer you would notice a blue 

 tinge creeping into the yellow, and turning it to 

 green; and by degrees the blue would become 

 stronger and stronger, till the green disappeared. 

 At last a crimson tinge would creep into the blue 

 and turn it to purple ; and this would be exactly 

 the same as the famous purple dye which the 

 ancient Romans valued so highly. 



The eggs which are laid by the purpura are 

 very curious indeed, for they are fastened down 

 to stones by little stalks ; so that each one looks 

 rather like an egg-cup with an egg inside it. 

 And inside each of these eggs are several little 

 purpuras instead of only one. 



PLATE X 

 THE SEA SNAIL (i) 



This is one of the very commonest of all the 

 shell-bearing molluscs. You may find it crawling 

 about in numbers all over the weed-covered 

 rocks which are left bare as the tide goes down. 

 Its shell varies very much in colour, for it is 

 sometimes bright yellow, and sometimes pale 

 yellow, and sometimes olive green, and some- 

 times brown, and sometimes almost black. In- 

 deed, you might almost think that there were 



