176 
LIFE AND HER CHILDREN. 
the balanus lives more securely than if he had re- 
mained a freely roving creature as we see him at 
i, Fig. 62 ; and the 
success of his re- 
tirement to a fixed 
life is proved by the 
countless number of 
acorn - shells which 
are found on every 
sea-shore. The lepas 
or barnacle with 
stalks (Fig. 61), you 
will see less often, 
for they live in deeper 
water attached to 
rocks or pieces of 
floating timber. 
Their history is the 
same as that of the 
Development of an Acorn Barnacle. acom-shell,only that 
1, A young acorn barnacle before it from the cement of 
has settled down. Spence Bate. their antennae they 
2, The grown-up acorn barnacle cut in / , i__ fl^oV.,, 
halfj *, head cemented to the shell; *, form lon g ^^ 
back ; m, position of the mouth ; c, cirrhi Stalks which fasten 
fringing the legs which sweep in the food ; the head to its sup . 
v, valves of the shell. Darwin. 
port. 
And here we must take leave of the Crustacea. 
We have really only made acquaintance with three 
branches; 1st, the ten-footed and stalk-eyed crus- 
taceans, the prawns, and crabs ; 2d, those with eyes 
fixed in the shell and breathing-gills fixed to the legs, 
the sandhoppers, and skeleton shrimps ; and 3d, the 
barnacles. But these by no means represent even 
