3 o8 THE SEAS 



sieves the mesh of which is determined by local bye-laws, 

 and only those animals which do not pass through the 

 meshes are allowed to be sold, the smaller ones being re- 

 placed on the beds. They are seldom sent alive to the 

 markets, but are usually boiled, often in iron vessels over 

 extemporized fireplaces on the sea shore. At Leigh-on-Sea 

 in the Thames estuary, the centre of one of the largest 

 cockle industries in the country, the cockles are arranged 

 in iron trays which are then placed in ovens the doors of 

 which are clamped, and the cockles then sterilized by 

 turning on steam for about five minutes at a pressure of 

 from twenty to forty pounds. As a result of this process 

 the soft parts come away from the shell from which they are 

 separated in large riddles which are swung backwards and 

 forwards until all the soft parts have dropped through the 

 meshes. The meat is then washed in fresh water and 

 dispatched to the market, either immediately or after 

 pickling in salt or vinegar. The shells are often ground 

 down to form grit for poultry. 



It is possible to judge the age of a cockle by examining 

 its shell, which is not added to regularly throughout the 

 year but, owing to the greater abundance of food and 

 warmer conditions, at greater speed during the summer 

 than in the winter. This difference in the rate of growth 

 of the shell is indicated by well-marked " winter " rings 

 and these have only to be counted to reveal the age of the 

 animal (Plate 109). This method is not, however, always 

 accurate because the growth of the cockles which has been 

 disturbed in any way — dislodged by storms or thrown too 

 far up the shore — is checked and " disturbance " rings, 

 not distinguishable from winter rings, are produced. 

 Since young cockle may extend the edge of their shells 

 at the rate of one to one and a half millimetres per week 

 it is easy to see how a few days' disturbance may interfere 



