Page:Beautiful·Shells·of·New·Zealand-Moss-1908.pdf/21

 Wherever animals or vegetables are crowded, disease appears. This is true of molluscs, and it is seldom worth while looking for a specimen fit for a collection where any particular kind of shellfish lives in great numbers. Animal and vegetable parasites will be found wherever shellfish are crowded together. For instance, a perfect cockle, or one good enough for a collection, will not be found on a cockle bank, but solitary ones must be looked for elsewhere.