THE OYSTER. 29 



from locomotor ancestors. There are many other 

 proofs that this has been its history, and that it has, in 

 comparatively modern times, learned to fasten itself to 

 rocks above the soft mud of our bays and estuaries,, 

 in order to avail itself of the rich vegetation ; that it 

 has lost its symmetry in order to fit it for this mode 

 of life. The oyster is a very ancient animal, and its 

 sedentary habits belong to the more modern part of 

 its history; although this change took place very long 

 ago, so far as human chronology goes, and fossil 

 oysters are found in many parts of the world. 



In order to understand the anatomy of the oyster, a 

 clear conception of the structure and significance of 

 its gill is most important. In ail the bivalve mol- 

 luscs the gills are very complicated, and they domi- 

 nate over the whole structure of the body in such a 

 way that an anatomical sketch of the animal is of 

 necessity little more than an account of the gills. A 

 thorough knowledge of the oyster-gill will not only 

 throw light on the purpose and use of all its other 

 organs : it will at the same time help us to understand 

 the great value of the animal as a means for making 

 the microscopic inhabitants of our waters useful, and 

 it will also show how well it is adapted for culti- 

 vation, and why it is impossible for natural oysters to 

 stock the whole bay without aid from man. 



The labor which is necessary before we can have a 

 clear, accurate picture of them, of their complicated 

 structure, their relation to other parts of the body, 

 their use and their origin, is considerable, but it is 

 well worth while, for the gills give us the key to the 

 whole significance of the oyster ; but this requires 



