70 CONCHOLOGIST’S COMPANION. 
The mechanism itself consists of the extensile 
member, which the animal propels at pleasure; of the 
reservoir in which the glue is collected, and of 
the external holes communicating with it,—while 
the action of the machine is seen, in forming the 
thread, analogous to that of making wire, by forcing 
the prepared material through holes of proper dimen- 
sions. ‘The secretion is an act too subtile for our 
discernment, except as we perceive it by the produce. 
But one thing answers to another: the secretory 
glands to the quantity and consistence required in the 
secreted substance, and the reservoir to its reception; 
while the outlets and orifices are constructed, not 
merely for relieving the reservoir, but for manufactur- 
ing its contents into a form and texture of great 
external use to the life and functions of the insect. 
But the texture is not only essential to the welfare 
of the inhabiting Mollusca, it also constitutes an im- 
portant article of commerce among the Sicilians; for 
which purpose considerable numbers of Pinna are 
annually fished up in the Mediterranean, from the 
depth of twenty or thirty feet. An instrument, called 
a cramp, is used for the-purpose: it is a kind of iron 
fork, with perpendicular prongs, eight feet in length, 
each of them about six inches apart, the length of 
the handle being in proportion to the depth of the 
water; for, notwithstanding the extreme delicacy of 
