376 THE OCEAN WORLD. 
mimals which prey upon it. In this its infant state, when it has just 
1eft the protection of the parent shell, the microscope reveals the 
young bivalve as having a perfect shell, and having an apparatus which 
is also for the time a swimming fad, ready to adhere to the first solid 
body which the current drives it against. This pad or cushion 
(which is represented in Fig. 169) is furnished with vibratile cilia, 
disposed round the young shell. Aided by the powerful adductor 
muscles, with which it is also provided, this cushion is projected 
through the water at the will of the young inhabitant, which has every 
facility for the purpose: it is even said to swim about near the 
mother, before final dismissal from the maternal protection, seeking 
shelter at the least alarm between the valves of the parent shell. The 
Fig. 169,—Young Oysters furnished with locomotive organs. 
pad disappears after the young oyster has finally attached itselt to a 
permanent bed of its own. 
Before this period of its life arrives, however, many are the 
dangers to which it is exposed: its enemies are numerous ; they lie 
in ambush for it in every cranny! It has to guard itself against 
‘eddies and currents, which would drive it out to sea, and mud banks, 
in which it would be smothered. Crustaceans, worms, and ccelente- 
rates, with other equally voracious marine inhabitants, prey upon it. 
Last, but not least, come the terrible and multiplied engines of the 
eager fisherman—and we can readily comprehend why it is that the 
oyster should be provided with such accumulated masses of ova. 
If the young bivalve is fortunate enough to escape all the snares 
and dangers we have enumerated, it grows rapidly. It is quite 
microscopic at the period of its discharge from the parent shell ; at 
one month it is of the size of a large pea, at the end of six months it 
is about three-quarters of an inch, a year after its birth an inch anda 
half to two inches, and finally, at the end of three years it has become 
