THE APPENDAGES, THEIR INTERRELATION AND FUNCTION 3°5 



the carapace. In Conchoecia borealis, as in many other species, development of the shoulders of the 

 carapace into sharp flanges provides hydroplanes which also contribute to uplift of the animal when 

 it is swimming. The main component of the swimming-stroke can thus be concerned with forward 

 propulsion. 



As has been pointed out, the antennal endopod shows sexual dimorphism. The tube-setae are 

 probably sensory, and in the male the hooked clasping-organ probably had a copulatory function. 



Fig. 4. C. borealis antipoda. A, transverse section through labrum and mandibular basis showing distal articular process of 

 coxa in labral socket; B, right mandibular coxa and part of basis from inside, ax, dorsal articular condyle of coxa; a.p, distal 

 articular process of condyle; a.p.m, anteroposterior labral muscle; b, basis; b.c, articular surface of basis and coxa; b.in, in- 

 cisor edge of basis; c, coxa; c.in, incisor edge of coxa; fl, anterior dorsal flange of coxa; Ib.g, posterior labral gland; Ib.s, wall 

 of labral socket. 



Labrum (Figs. 2, 4, 7, 8, 10) 

 The labrum is well developed and filled with gland-cells. It is usually described as being helmet- 

 shaped. In section, its ventral surface is flattened and its dorsal surface rounded (Fig. 4 A). It arises 



