452 
TRANSFORMATIONS OF INSECTS. 
parts of the crab, from their simplest to their adult and most 
elaborate condition. 
The embryo, when it first quits the egg, is enclosed within a 
general tunic, which embraces each individual member, and is 
conformable to the whole animal. The tunic is exceedingly trans- 
parent, and the hairs of the young immature crab and the horn- 
like processes which characterise the carapace, are folded down 
and compressed. The crab swims about for a few hours in this 
state, and then liberates itself by throwing off the portion of tunic 
which covers the head and the part of the body which gives off 
the long legs. The tunic upon the jointed tail-like end is cast off 
some hours afterwards. (Page 454, Fig. 1.) 
The following terms are used to distinguish the portions of the 
body of the Crustacea . The tail-like long body is called the pleon , 
from TrAeo), to navigate, being that part of the animal which sup- 
ports the limbs by which it swims about ; and the swimming 
limbs are called pleopoda. The tail end is the telson. The portion 
which supports the walking legs is called the pereion , from Trepcuoco, 
to walk about ; and the legs are termed pereipoda. This portion 
is hidden by the carapace in the young state, and this last-named 
part is what is familiarly considered to be the head. 
When freed from the tunic, the animal sports and gambols in 
the water partly by the action of the entire pleon, and partly by 
the great feeler legs attached to the pereion. The carapace is seen 
to be armed with a long projecting beak or rostrum, and a spine- 
like portion projects from the back. (Fig. on page 453.) In this 
early stage the dorsal spine or that on the back, is no mere 
ornament, but possesses a specific use in supporting the heart in 
its position. The carapace is attached to the pleon by a mem- 
brane, and there is an opening in it on either side, so as to 
admit a stream of water into the branchial cavities. The cara- 
pace is compressed in front, and the eyes are prominent, and are 
fixed upon a short stalk. 
In the youngest stage, and in the crab when escaped from the 
tunic ( Zoea — for the crabs, unlike many other Crustacea , do not go 
through the nauplius form) there is a pair of appendages in front 
which represent the antennae, and there are some hairs upon them, 
which become gradually developed into the organ of hearing. 
