. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. 3o6 DISCOVERY REPORTS ventrally in front of the mouth and projects forward below and between the shafts of the antennae. The vertical posterior surface forms an anterior boundary to the oral atrium (Fig. 8). The atrium is bounded laterally by the mandibles, paragnaths and maxillules, and leads antero-dorsally into the oesophagus, which is directed slightly forward and upward. The posterior wall of the labrum usually bulges back to some extent, between the mandibular coxae. It is, however, provid
. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. 3o6 DISCOVERY REPORTS ventrally in front of the mouth and projects forward below and between the shafts of the antennae. The vertical posterior surface forms an anterior boundary to the oral atrium (Fig. 8). The atrium is bounded laterally by the mandibles, paragnaths and maxillules, and leads antero-dorsally into the oesophagus, which is directed slightly forward and upward. The posterior wall of the labrum usually bulges back to some extent, between the mandibular coxae. It is, however, provided with antero- posterior muscles (Fig. 4 A, ), which can draw it forward and so increase the volume of the atrium. It bears a median patch of short, fine, dorsally directed bristles (Fig. 8). Ventrally to the oral atrium, a thin flat surface, with thickened cuticle, extends back horizontally from the labrum like a shelf. This may be termed the labral lamina (Fig. 8, ). Laterally, the posterior edge of this lamina takes the form of comb-like structures. The whole posterior surface of the labrum and the labral lamina is supported by sclerites continuous with the ventral sclerite system of the animal. The labrum contains two systems of glands. The anterior of these consists of a number of large unicellular glands, closely packed and running dorso-ventrally. Their openings are evenly spaced over the ventral and lateral walls of the labrum. The openings can only be seen clearly in heavily stained material ( with chlorazol black), when they appear as small crater-like depressions. The second system is a paired compound gland, the two components of which lie partly within the posterior part of the labrum (Fig. 4 A, ), but extend into the body on either side of the oesophagus. These latter glands open through the posterior wall of the labrum into the oral Fig. 5. C. borealis antipoda. Right mandible from inside, b, basis; , incisor edge of basis; c, coxa
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