io8 
LIFE AND HER CHILDREN. 
Iv 
a spring of a jack-in-the-box, and drives the covering 
valve up unless it is forcibly pulled down. This, 
however, can be done by 
a strong muscle (ins) 
which lies within the 
valves, and has one end 
fastened to the upper and 
the other to the lower 
valve, so that by con- 
tracting this muscle the 
oyster can pull its shell 
together with a snap 
when danger is near. 
Close round this muscle 
lies the body of the ani- 
mal between the two 
flaps of the mantle (in ;;/). 
Lifting up the upper flap 
you will find, edging the 
body and growing to the 
mantle, a delicate transparent frill (g) of four striped 
bands, these are his gills or breathing apparatus. 
" The fringes that circle its body, 
Which epicures think should be cleared, 
Are the animal's lungs for 'tis odd, he 
Like a foreigner breathes through his beard." 
The stripes are tubes which run up and down 
each fold, and through them flows the sluggish 
colourless blood of the oyster, so that as the gills lie 
bathed in water, the blood takes in oxygen through 
the delicate membrane, and flows back to the body 
purified and refreshed. The remainder of the oyster 
* Ostrea edulis. 
An Oyster * lying in the shell. 
j, Shell ; ;;/, lower half of mantle ; 
;;/, a piece of the upper half; g, 
breathing gills ; h, heart ; Iv, liver ; 
Ip, lips ; o, opening of mouth ; a, 
anus where refuse is thrown out ; ms, 
muscle holding shells together ; c, 
elastic cushion forcing them apart. 
