148 Canadian Record of Science. 



spontaneously opens, it is a sign that it is dead. But 

 here several questions may be asked; for instance how 

 does the Oyster know that a starfish is coming? And 

 if it is able to know and to shut up, how do starfish 

 live ? 



Oysters are apparently devoid of sense organs; never- 

 theless if the edge of the mantle be examined it will be 

 found to be fringed with innumerable little tentacles in 

 which there is deposited a certain amount of pigment. 

 If now a healthy Oyster be observed whilst it is 

 feeding with open valves in a tank, it will be seen that 

 when the slightest shadow falls on these tentacles the 

 valves are instantly closed. The tentacles enable their 

 possesser to distinguish between light and shade, and it, 

 is by means of its sensitiveness to slight shadows, that 

 the Oyster learns to close in time. 



The starfish, however, manages to destroy quite a 

 large number of Oysters. Armed as this creature is 

 with thousands of minute suckers, it is able whilst hold- 

 ing firmly on to the ground with some of these to 

 forcibly raise the upper valve of its victim by means 

 of the remainder which adhere firmly to the ground 

 in the neighbourhood. It seems incredible, when one 

 reflects what force is necessary to insert a knife be- 

 tween the valves of a closed oyster, that a starfish should 

 be strong enough to forcibly pull them apart. But it 

 is nevertheless true, for the starfish has staying power, 

 and the long steady pull lasting for a quarter of an hour 

 or more, effectively overcomes the resistance of the oyster, 

 although the latter is able to withstand a much greater 

 force if exerted for a shorter time. Nevertheless, the 

 bigger the Oyster the bigger must the starfish be which 

 opens it, and from the size of the starfish found on the 

 Malpeque beds it is not probable that they can do much 

 damage to the larger Oysters, and we may perhaps con- 

 clude that the Oysters are safe from their attack once 

 they have passed their third or fourth year. 



The Oyster possesses a simple alimentary canal. A 



short gullet leads into the stomach into which two 



groups of branched tubes, termed the liver 



