318 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



fig. 21) is the largest appendage in the body. It consists 

 of seven segments (or podomeres). A comparison with 

 the third maxillipede indicates that the two proximal 

 segments belong to the protopodite, and the remaining 

 five to the endopodite. There is no exopodite present. 

 The seven segments have the same names as the similar 

 parts in the third maxillipede. With the exception <>l 

 the second and third segments, which are fused together 

 to form the basi-ischium (B-I.), all the parts are freely 

 movable. The basi-ischinm has a thin groove running 

 around it, which marks the separation of this fused 

 portion into its two constituent parts. This groove is 

 known as the fracture plane because it is at this point that 

 the animal fractures the limb during the process of self- 

 amputation (see section on Autotomy). The two distal 

 segments of the limb are slightly modified to form the 

 pincer which constitutes an effective prehensile organ. 



Each of the movable segments swings in a different 

 plane, so that the combined movement of the whole 

 appendage is a very complete one. The coxopodite (C.) 

 articulates with the body by means of two hinges, one 

 being dorsal (PL III., fig. 21, d.) and the other ventral 

 (v.). The dorsal hinge is attached to the antero-ventral 

 corner of the epimeron of the fourth thoracic somite, and 

 the ventral hinge articulates at the postero-lateral corner 

 of the sternum of the same segment. Thus the motion of 

 the coxopodite is in a horizontal plane, moving backward 

 and forward. The fused basi-ischinm (B.-I.) articulates 

 with the coxa by an antero-dorsal (d 1 ) and a postero- 

 ventral hinge (v l ), and the movement is upwards and 

 downwards in a plane making an angle of about 45° with 

 the vertical. The meros (M .) has very little movement. 

 Its two hinges are antero-dorsal (d 2 ) and postero-ventra] 

 respectively (v 2 ), and the small degree of movement of 



