86 
Zoology. 
Order 1. Cirripedia. — The barnacles would, at a first 
glance, hardly be regarded as Crustacea at all, so much 
modified is the form, owing to their fixed, parasitic mode 
of life. The barnacle is, as in the common sessile form 
(Fig. 100), a shell-like animal, the shell composed of sev- 
eral pieces, with a conical movable lid, having an opening 
through which several pairs of 
long, many-jointed, hairy ap- 
pendages are thrust, thus cre- 
ating a current which sets in 
towards the mouth. The com- 
mon barnacle (Balmitis iaJaiioi- 
des) abounds on every rocky 
shore from extreme high-water 
mark to deep water, and the 
student can, by putting a group 
Fig. 100. -a barnacle. Baianus of them in sca-watcr, obscrvc the 
porcatus. Natural size. opening and shutting of the 
valves and the movements of the hairy appendages. 
The metamorphosis of the barnacle is remarkable. After 
leaving the egg, it swims about as a minute Nauplius or 
larva (Fig. 101), with three pairs of legs. Finally the larva 
attaches itself by its antennae to some rock, and now a 
strange transformation follows. The body and legs (the 
