EXTERNAL ANATOMY OP THE COLEOPTERA. 
33 
Pro6ternum of thorax of 
D. marginalia. 
parts, viz. (Fig. 7) a, the 
are considered each to be 
normally composed of four 
separate pieces, — the prce- 
scutum, scutum, scutellum, 
and post-scutellum j but 
these are all joined together, 
with no trace of suture in the 
pronotum of the Coleoptera. 
The prosternum bears the 
two front (or anterior) legs, 
and is divided into three 
sternum ; b b, the episterna, 
and c c, the epimera. The 
coxa, or hinge-plate of the 
leg, is seen at d ; e is the 
trochanter ; f, the femur, 
or thigh ; g, the tibia, or 
shank ; and h, the tarsus, 
or foot, of which the joints 
are separately numbered. 
The first three joints in the 
male of Dytiscus marginalia 
are widened into a round 
plate, provided with suckers 
beneath, as will be seen by 
Fig. 7 ; in which, with the 
other cuts of the thoracic 
segments, only one of the 
limbs is represented. All 
these figures are, of course, 
considerably magnified. 
The mesothorax, which 
bears the wing-cases, or elytra, and the intermediate 
Fi*. 8. 
a. Mesothorax of D. marginalia, 
seen vertically. 
b. Ditto, seen from above. 
