LIGIA. 75 



for eopulatory 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 (PL II., 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 styli- 

 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. 



Body Wall, Muscular System and Body 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 spines and setae in many regions of the 



