130 SCIENCE FROM AN EASY CHAIR 



may be compared to the leaves of the notebook. Suppose 

 there are twenty-six leaves, then the outermost leaf on 

 each side corresponds to the two soft living membrane- 



d 



FlG. 28. An oyster with the right-side shell removed ; c, 

 the pearly inner surface of the left-side shell ; d, the 

 horny outer layer projecting beyond c ; a, the thick 

 edge of the " mantle "-flap of the left side ; b, the 

 thick edge of the mantle-flap of the right side thrown 

 back towards the centre, so as to show what underlies 

 it ; e, notch in the surface (pulled a little upwards and 

 forwards) where the ligament is formed ; h, the hinge 

 urface, where the removed shell rested on the left-side 

 shell ; g 1 to g*, the four gill-plates or flaps, two right 

 two left the so-called beard ; /, the four correspond- 

 ing lip lobes : the mouth lies deeply between the 

 second and third that is between the right pair and 

 the left pair ; m, the central shell-muscle, which runs 

 from one shell to the other. 



ous flaps which secrete the two shells or covers of the 

 oyster and lie closely on them (a, b, Figs. 28 and 30); 

 the next two on each side (rather shortened leaves, folded 



