206 ANNULATA. 
part of the exterior partially shut in. In many Crustacea 
the part of the body here covered by the carapace is divided 
into head and thorax, and in Wephrops the line of junction 
is shown by a cervical suture passing down laterally and 
obliquely from the mid-dorsal line. ; 
Fig. 130.—LATERAL VIEW OF Norway LOBSTER (Right) x 3. 
(Ad nat.) 
Branchial Cervical 
rst Abdominal Segment. Plate. 
N 
: Ne 7 : 
¢ oe t \ a ; 
/ Swimmeret. wy nt 4 ere ee 
| Telson. } ) \\ " 3rd Maxillipede. 
6th Abdominal Segment. a ist Leg. 
The third portion of the body, behind the carapace, is 
called the abdomen. In this region there are several 
sclerites movable on each other and they are found to 
correspond with the metameric segments of the body. 
Each abdominal sclerite is roughly in the form of a ring. 
The dorsal part is called the ¢exgon, the ventral narrow 
part is the s¢ernon, and from the junction there hangs down 
laterally the pleuron. Just inside the pleuron there is an 
appendage on each side. Each abdominal sclerite is 
fastened to its fellows in front and behind by dorsal and 
ventral arthrodial membranes and laterally by a pair of ball- 
and-socket joints, which allow of movement only around 
the axis through them. The sclerites overlap dorsally those 
behind them. The last (7th) abdominal sclerite is flattened 
and bears no appendages: it is called the ze/son. . The appen- 
dages of the abdominal sclerites are termed szwzmmerets for 
they are mainly used for swimming. They consist typically 
of a basal piece, the proftopodite, bearing two paddles, the outer 
