TEE PURPURA. 



197 



men. Two hundred and ten species are known, extending from low water to fifty fathoms. They 

 are world-wide in their distribution. 



In Purpura, the shell is striated, or tuberculatecl, with a short spire and a large aperture, 

 slightly notched in front, the inner lip being flattened. 



Behind the head of Purpura lapillus, the only species that Britain possesses, is a recep- 

 tacle containing a white fluid, which, on exposure to the air and light, reaches a brilliant 

 tint through several intervening gradations of yellow, green, and blue.* The 

 dye so obtained is made permanent without difficulty ; but, although it was 

 formerly used in Irish manufactures, it has long since ceased to be so employed, 

 perhaps through not being procurable in sufficient quantity to make it worth 

 collecting. The egg-bags of the Purpura lapillus, commonly called the " Dog 

 Periwinkle," are deposited on the surface of rocks, or stones, or shells, united in 

 considerable numbers to a common membrane, on which they stand erect like so 

 many oval cups, each cup containing an embryo. Here the young Purpurce remain 

 for some months before the cup opens, and when this happens they do not all take 

 immediate advantage of the new-born privilege, but some of them prefer remaining 

 where they are for a time, in ease and comfort, till they acquire sufficient strength- PURPURA LAPILLUS 

 and courage to leave the protection of their cells. 



Purpura, like Littorina, crawls about on the shore between watermarks, and seldom 

 ventures under the lower tide-mark. It is very destructive to the mussel-beds. Gliding stealthily 

 among the sea-weed and stones, it seeks its prey, and woe to the small Winkle, Limpet, or Trochua 

 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 its trunk, never leaves it until all the soft parts are trans- 

 ferred to its own capacious stomach. But even where no aperture or door leaves the smaller molluscs 

 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 attached to a stone, or a bivalve tenaciously holding its 

 shell closed, he will manage to perforate the shell, and, through the hole, to draw forth the quivering 

 substance. Mr. Spence Bate relates, that by way of experiment, he placed a 

 Purpura in a vessel of sea-water in company with a Mussel, and observed the 

 result. In a short time the Purpura, finding that the Mussel was not at all 

 open to his advances, and that the valves of the shell were so firmly drawn 

 together as to leave 110 chance of effecting an entry between their edges, 

 began to think of attacking him from without. Seeking a portion of the 

 outer surface free from epidermis, he commenced boring. His human 

 observer, repudiating the policy of " non-interference," removed him, and 

 turned the Mussel over, placing that valve uppermost which was most covered 

 with the horny protection. The creature soon managed to turn over the huge 

 body and shell of the Mussel, and resumed his operations at the point where 

 he left off when disturbed, and he did this repeatedly after similar interrup- 

 tions. At last, quite satisfied that the breach would in time be effected in 

 this way, Mr. Bate resolved to wait no longer for the process, but at once 

 to give the voracious sea snail an opportunity of satisfying its appetite at a 



smaller demand of exertion from itself and of patience from its observer. To this end he cut the 

 muscles of the bivalve, so as to deprive it of the power of keeping its valves closed. Its fate 

 was thus accelerated ; it was now at the mercy of its enemy. The latter no sooner perceived the 

 valves open than, leaving his former work of boring, he seized his advantage by inserting his trunk 

 between the valves, not in this instance realising to the full the general rule, that the enjoyment 

 of an acquisition is increased in proportion to the difficulty and trouble of obtaining it. When not 

 so unexpectedly assisted, however, the hungry Purpura exhibits much patience, occupying himself 

 for a couple of days in making his way through a mussel-shell. After gorging himself with a large 

 portion of its contents, he lies for weeks without attempting to procure a fresh supply. 



VVIU'UKA 1'ATULA. 



The animal can always be induced to discharge its dye by pressing on the operculum. 



