3/6 THE OCEAN WORLD. 



animals which prey upon it. In this its infant state, when it has just 

 left 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 pad, 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 itself 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 coelente- 

 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 

 u about three-quarters of an inch, a year after its birth an inch and a 

 half to two inches, and finally, at the end of three years it has become 



