104 ISOPODA. 
rally nearly equal in size,* movable, and with the pos- 
terior lateral angles generally extending backwards over 
the base of the legs. The large dorsal are of each seg- 
ment is accompanied at each side with a small but distinct 
plate (epimeron of M. Milne Edwards), on the under- 
side of which the corresponding leg is affixed. These 
scale-like pieces, which are the first joints of the legs, 
are often soldered to the dorsal arc, their limits being 
indicated by impressed lines; but in other cases, as in 
Rocinela, Aiga, &c., they are very distinct, forming 
acute lateral points to the segments. The legs are, for 
the most part, of small size, and more or less uniform 
in shape: they are (generally) affixed to the lateral 
margins of the underside of the body, the basal joint 
being long and lying flat on the breast, its extremity 
being brought into contact with the extremity of the 
basal joint of the opposite leg, whilst the second and fol- 
lowing joints of the leg are affixed at an angle and 
directed outwards. This arrangement of the limbs is 
especially marked in the anterior pairs, which thus put 
on the appearance of outer mouth-organs. The legs 
generally terminate in hook-shaped fingers, which, espe- 
cially in the parasitical species, are of considerable size 
and power. In the arrangement of these limbs there 
may, however, notwithstanding their general conformity, 
be observed somewhat of the division into series which 
we have alluded to in our introduction to the Amphipoda 
(vol.i. p.7). Thus in Arcturus the first pair, the second, 
third and fourth pairs, and the three posterior pairs, con- 
stitute distinct series both in structure and function, 
whilst in Serolis and Apseudes the first pair is as greatly 
* In Tanais, which in some respects might almost be regarded as the link 
between the Isopoda and the Squillide, the first segment of the body is of 
large size, and is confluent with the head. 
