THE MAGILUS ANTIQUUS. 291 
Wien the sea is quiet, these little creatures, 
Like little wanton boys that swim on bladders, 
appear in vast shoals on the surface, but as soon as the 
wind ruffles the ocean, or an enemy approaches, they at 
once empty their air-cells, contract their float, and sink to 
the bottom, pouring out at the same time a darkened fluid 
like that of the Aplysia or the Murex, which no doubt 
serves them as a defence against 
their foes, and, according to Lesson, 
furnished the celebrated purple of 
the ancients. The Janthine inhabit 
the Mediterranean and the warmer 
regions of the Atlantic, but especially towards the close of 
summer they are frequently drifted by the Gulf Stream to the 
west coast of Ireland. 
While the vast majority of the gasteropods either creep or 
swim, some are doomed to the sedentary life of the oyster, 
and remain for ever fixed to the spot where 
they first attached themselves as small free- 
swimming larve. Thus the Magilus an- 
tiquus, which in its young state presents all 
the characters of a regular spiral univalve, esta- 
blishes itself in the excavations of madrepores, 
and as the coral increases around it, the Magilus 
is obliged, in order to have its aperture on a 
level with the surrounding surface, to construct 
a tube, lengthening with the growth of the 
coral, As the tube goes on increasing, the 
animal abandons the spiral for the tubular part of the shell, and 
in the operation it leaves behind no partitions, 
but secretes a compact calcareous matter which 
reaches to the very summit of the spiral part, so 
that in an old specimen the posterior part of the 
shell presents a solid mass. 
The Siliquariz are generally found embedded 
in a similar manner in sponges or other soft 
bodies, while the Vermetus, or Worm-Shell, usually 
attaches itself, like the Serpule, to rocks, coral-reefs, or 
shells. 
Ky 
Murex haustellura. 
Magilus antiquus. 
Worm-Shell. 
