OF THE GULF OF MANAAR. 
99 
hold for life of the true oyster (Ostrea). The byssus is 
formed of a miinber of separate threads thrown out one by 
one and cemented to the rock or other hard substance each 
thread separately at its tip which is a flattened oval and the 
several threads are so directed by the animal that the hold 
may be spread. Being thus spread out into separate threads 
at the end furthest from the animal, the byssus converges 
into one cable before union with the animal. Each thread 
which goes to make up the cable being necessarily thrown 
out from the animal, the cable end is at fii'st weak, and 
strengthened as the number of threads is increased. These 
are multiplied at will according to the necessity of the 
animal, as few as eight or ten being noticed on one, and 
as many as fifty on another. Once having cemented the 
spatulous end of a thread of the byssus, the pearl oyster is 
not capable of withdrawing that thread, it can only shed its 
whole byssus at the point where the cable end of it is attached 
to the animal. Whether it sheds its byssus, or the byssus 
is forcibly torn out of it, or the thread ends are cut, the 
animal is capable of forming a new byssus. It is a common 
thing for the threads of the byssus to be bitten through by 
shrimps or crabs, and no clump of young pearl oysters can 
be taken up from the sea without exhibiting on their shells 
the shed and cut byssi of their brethren that have been 
attached to them, and the shed bt/ssi and those that have 
been forcibly torn out by the root are readily distinguishable 
from those that have been cut by crabs, &c. The fact that 
the young shed and reform them more often than the old 
indicates that they are more migratory at that age than 
when older. 
I have again and again applied prolonged steady tension, 
and also in different directions, to see if any single thread 
would yield its hold, but it is evidently cemented so that 
it cannot let go. If it could let go, it would surely do so 
and withdraw itself into its shell before suffering itself to be 
