THE OYSTER. 47 



Every part consists of cells, which are united into 

 organs, in nearly the same way that these are united 

 to form the oyster; and in order that what I shall say 

 about its development from the egg may be intelligible, 

 this fact must be held clearly in mind. 



Each cell is a minute portion of living matter, with 

 an individuality of its own, like the individualities of 

 the soldiers which form the regiment. 



The properties of each organ are due, in part, to the 

 way in which the cells are arranged, and in part to the 

 properties of the cells themselves, for the cells which 

 enter into one organ may be quite different from those 

 which enter into another. 



Each of the cells which form the glandular surface 

 of the mantle is itself a gland, and is quite different 

 from a muscle cell, so that, in a certain sense, the 

 activity of the mantle in forming the shell is the sum 

 of the activities of its cells, just as the evolutions of a 

 regiment are the sum of the actions of the soldiers, 

 but a regiment can do many things which would be 

 beyond the power of an unorganized mob, and the 

 formation of the shell is due to the activity of the 

 mantle as a whole. 



In an adult oyster we have gland cells in the mantle, 

 muscle cells in the muscles, nerve cells in the nervous 

 system, ciliated cells in the gills, and so on ; but if we 

 study the animal at earlier and earlier stages, we find 

 that these distinctions disappear, until, in ultimate 

 analysis, all the cells are alike so far as the microscope 

 tells us. 



