Tank No. 22. 
59 
Fig. 98. Two specimens of Ostrea edulis on a 
stone, 1/2 nat. size. 
male and female. The eggs may number several millions and ripen in 
summer. The young live in the mantle - cavity of the parent, till their 
shell is sufficiently strong to allow them to "swarm” and fix themselves. 
The Oyster lives in all seas with the exception of the Baltic, and 
often makes its way up into the rivers. In Europe and North America 
they are artificially reared 
on "Oyster-beds”, as they 
are not only a luxury but 
(especially in England and 
America) one of general 
consumption. The number 
of Oysters eaten in Eng¬ 
land in a year is said to 
be 2000 millions, while 
America consumes 4000 
millions. Artificial culture 
was already practised by 
the ancients; at the tables 
of Imperial Rome oysters 
were never wanting, and 
epicures declared the best 
to come from the lake Lu- 
crinus at Bajae. Brindisi, 
too, was one of the prin¬ 
cipal localities, as it is 
even at the present day, for 
the culture of the Oyster. 
The Edible Mussel, 
Mytilus edulis (Fig. 99), 
has the well known al¬ 
most triangular, blue-black 
shell. The animal has a 
so-called 6ys$ws-glandwith 
which it produces long 
horny threads, which fasten it to rocks and woodwork, so that the 
roughest sea or strongest currents cannot dislodge it. If it wants to 
leave its home, it produces a new byssus with its finger-like foot and 
then it tears the old byssus away; by repeatedly doing this it moves 
very slowly onwards. It flourishes best in northern seas, where it is 
extensively collected and cultivated; for this purpose trees are let down 
into the water and from time to time drawn up, and the Mussels adhering 
are removed. 
Pinna (Fig. 100) is a large, thin-walled, club-shaped shell, which is 
fixed in the mud by its narrow end. It also possesses a byssus which, 
however, is much longer and composed of finer threads than that of the 
Mussel. These silken threads were formerly used for the manufacture 
of gloves, stockings and even entire garments; in the 18 th century there 
existed at Naples and Sicily large works for spinning them. The 
shells of Pinna also yield occasionally pearls, which, however, are of very 
Fig. 99. Three specimens of Mytilus edulis, at¬ 
tached to a piece of rope, 1/2 nat. size. 
