72 Proceedings of the Royal Society of Edinburgh. [Sess. 
more than a right angle, and in the opposite direction to that at the 
ischio-flexure, occurs at the carpo-propodal joint. In the same plane and 
in the same direction the dactylopodite flexes on the propodite. The 
combined angular movement of the last two joints, which we might call 
for shortness the “ propodo-flexure,” equals two right angles. Thus the 
propodo-fLexure is complementary to the ischio-flexure ; by means of it 
the laterally directed dactylopodite can be made to point medially like 
the basipodite. 
After death there is usually some flexion of the carpo-propodal articu- 
lation, and Boas (1883) on comparative grounds singled out the high 
Fig. 2. — View of disarticulated fourth (free) thoracic segment of Ligia as seen from the front. 
In A (squatting position) there is acute flexion at the ischio-flexure. In B (position of limbs 
after death in distilled water) there is flexion at the basi-ischial articulation, the limb being 
extended at the ischio-meral articulation ; at the carpo-propodal articulation there is also flexion. 
degree of flexion possible at this joint as of special systematic value in 
grouping together the orders now included under Peracarida. As we shall 
soon see, however, to single out this characteristic alone as a peculiar feature 
of the peracaridan limb is trivial. At the same time it is of interest to 
note that in both the ischio-flexure and the propodo-flexure the more 
proximal of the two constituent joints is functionally the more important. 
The Dactylopodites differ in many respects from the other limb 
segments. Like the dactylopodites of a shore-crab, they tend to be dark 
red in colour (see the last communication of this series), with a thicker and 
more heavily calcified wall and with less soft-tissue content than the more 
proximal segments. The latter are provided with chromatophores and 
with tactile hairs; the dactylopodites have neither. Each carries on its 
ventral aspect, arranged in the line of the post-ischial axis, two attenuated 
