22 GLIMPSES OF NATURE. 



companion valve, the neighbour-impression. Between 

 the two valves of the shell, then, there stretches this 

 strong band of muscular fibres ; so strong that it 

 requires the deft hand of the oyster-opener to detach 

 them. This muscle which closes the valves and keeps 

 them shut is called the "adductor;" and while our 

 oyster has but one, the mussels themselves possess 

 two. It is a voluntary muscle this of the oyster, 

 and quite as much at the command of the animal 

 as your own biceps is placed under your behest. 



But the adductor muscle of the oyster is not an 

 organ which is frequently in use. If the shell is 

 closed by its action, how, you inquire, are the valves 

 opened ? Look once again at the empty shell. You 

 observe at its beak or apex the remains of a brownish 

 substance. That is the " ligament" of the shell. It 

 is an elastic band, which is put on the stretch when 

 the shell is closed by the adductor muscle. If that 

 muscle relaxes, you see what will happen. The 

 elastic ligament will come into play, and by that 

 elasticity will keep the shell open. 



Now, as an open shell is the oyster's natural con- 

 dition, we can note in this contrivance a saving of 

 power. The shell is kept unclosed by the purely 

 elastic and mechanical action of the ligament. The 

 oyster has no need to bother itself over this duty. 

 But it is when the more unusual work of closing the 

 shell has to be accomplished that the vital and 

 muscular act comes into play. Then the muscle acts, 

 and " shuts up shop," so to speak, without delay. 

 Nature is always economical in her distribution of 

 power, and our oyster is kept gaping without the 

 expenditure of any vital activity. 



I may not linger to-day to tell you of the gills of 



