LIGIA. 75 
for copulatory purposes. The superior lobe of the first 
pair of pleopods also may be modified slightly for copula- 
tory purposes. The third, fourth, and fifth pairs of 
pleopods are very similar in character, the third pair being 
the largest. 
The uropoda (PI1.I1., fig. 14) are situated at the posterior 
edge of the sixth abdominal segment or telson, the pleural 
regions of which are produced posteriorly, thus forming a 
small sinus in which the uropods can bend laterally. 
Each consists of a stout basal joint which is 
widest in the middle and truncated distally. The middle 
region is thick, narrowing off sharply to the 
outer edge, and slightly to the inner edge, which is 
adjacent to that of its fellow. Distally, two setose styl- 
form processes arise. These are about twice the length 
of the basal portion. During life they are carried in a 
diverged position, being separated vertically by a wide 
angle. The inner style has a well-developed terminal 
spine which is trailed over the ground, and is probably 
of a sensory nature, as it has similar nervous connections 
to the sensory bristles of the antennae. 
Bopy Wau, MuscuLar SysTEM anpd Bopy Cavity. 
The body wall consists of three layers, the outer 
cuticular layer, the hypodermis and the connective tissue. 
The cuticular layer is composed of a thin cuticula resting 
on a thicker layer of chitin, in which two distinct layers 
can generally be observed (Pl. IV., fig. 3). The chitin is 
impregnated with salts of calcium, which cause it to have 
a fairly resistant and brittle texture. Between the segments 
the chitinous layer is thin. In the middle region of the 
dorsal side the intersegmental membrane does not dip 
deeply into the tissues, as it does at the sides. The 
cuticula bears spies and setae in many regions of the 
