THE APPENDAGES, THEIR INTERRELATION AND FUNCTION 



3°7 



(Fig. 4, c.in) extends into the oral atrium. As mentioned above, it forms a lateral boundary to the 

 atrium (Figs. 7 and 8). Anteriorly at this lower end the coxa is produced into a distally directed 

 process (Fig. 4 B, a.p), which Skogsberg (1920, p. 570) describes as more or less triangular and 'against 

 which the endite on the following joint rests with an antero-inner edge'. Skogsberg also refers to the 

 term 'Zahnhocker' adopted by Claus (1891) for this process. In fact the structure is much more 

 rounded than is suggested by these descriptions and is directed (it should be noted) much more nearly 

 parallel to the longitudinal axis of the coxa than is shown in the figures given by Claus (1 891, pi. xxn, 

 figs. 6 and 15). The statement that the endite of the following joint rests on it is quite erroneous. 

 No doubt Skogsberg based it upon observations of isolated mandibles. Examination of the appendage 

 in situ and in section, shows that the process fits exactly into a thickened socket, which is part of the 



Fig. 6. C. borealis antipoda. Diagrammatic anterior view of a thick transverse section through mandibular region. (Antennal 

 shafts omitted to show mandibular coxae.) a^f.o, base of antennules and frontal organ; a 2 , antennal socket; a.c, dorsal 

 articular condyle of mandibular coxa; a.p, distal articular process of mandibular coxa; fl, anterior dorsal flange of mandi- 

 bular coxa; ist, isthmus linking body with carapace; lb, labrum; mn.b, mandibular basis; mn.c, mandibular coxa. 



sclerite framework supporting the oral surface of the labrum (Fig. 4 A, a.p and Ib.s, Fig. 8). The 

 projection of this peg into the socket in the labrum is sufficiently deep to make it difficult to remove 

 the appendage during dissection. The mandibular coxa is thus restricted in its movement to rotation 

 about the axis formed by this articular process and the dorsal condyle. This axis, in fact, coincides 

 fairly accurately with the anterior margin of the area of articulation of the coxa with the body 

 (Fig. 4 B). In relation to the body of the animal, the axis of rotation of the coxa extends upwards, 

 sloping slightly outwards and backwards (Figs. 2 and 6). 



The mandibular musculature has been figured by Muller (1894, pi. 55). The extrinsic musculature 

 of the coxa is in fact very much more complex than is shown in his figures. Full details of this 

 musculature will not be given here, but it is significant that the arrangement of the muscular elements 

 is such that they will rotate the coxae about the axes which result from their bicondylar suspensions. 

 The anterior dorsal muscles originate near the hinge-line of the carapace and are inserted on the 

 flanges anterior to the dorsal condyles. Since the axes of rotation of the coxae slope markedly out- 



