514 THE VOYAGE OF H.M.S. CHALLENGER. 



is excavated for the reception of the large visual organs, and centrally the structure of 

 the integument is reduced to considerable tenuity, through which a longitudinal fissure, 

 like a closed aperture, exists. At the base of the joint on the inner side there is a 

 considerable hollow enlargement with a narrow aperture on the inferior surface, which 

 is protected by a strong but not very prominent ridge. At the opposite extremity of 

 the same joint there is a thin semi-membranous spot that is also probably associated 

 with the acoustic apparatus. 



The second pair of antennae appears to spring from the metope or facial wall, which 

 in both sexes is membranous. The phymacerite exists in the form of a conspicuous 

 tubercle, flattened transversely, the opening of which is on the posterior surface close to 

 and at the end of a long groove in the lateral wall, which is larger and more conspicuous 

 in the female than in the male. 



The cheiloglossa is continuous with the epistoma, which in the male is membranous 

 and perpendicular. The metastoma consists of two plates separate from each other 

 longitudinally and obliquely, and produced anteriorly and laterally in the form of 

 large fleshy plates, that cover not only the oral opening but overlap to a considerable 

 extent the posterior lateral margin of the cheiloglossa, so as to cover up and entirely hide 

 the mandibles in the male. In the female the mandibles are seen at the side apparently 

 thrown very far back. In the two sexes the conditions are different, the epistoma in the 

 female is strong and calcified, and the cheiloglossa projects conspicuously beyond its 

 margin, and anteriorly presses between the mandibles. Hence these latter organs appear 

 to have no external biting power. They lie protected between the lateral margins of the 

 anterior and posterior labra, where apparently they have no power to act untfl the 

 projecting cheiloglossa, which intrudes itself between them, moves from its position, and 

 acting as a tongue, guides the food to its place both for mastication and deglutition. 



The third or middle pair of pereiopoda in the female carries the oviduct, which is 

 surrounded by a fringe of hairs. The fifth or posterior pair in the male carries the penis, 

 the passage of whicb is by a large round foramen. Behind this last pair of legs a 

 prominent projection like a broad flat tooth, more decided in the male than in the female, 

 rises from the posterior angle of the ultimate somite of the pereion and rests against the 

 inflected margin of the carapace. 



The anterior pair of pleopoda differs in the two sexes. In both they are large, 

 foliaceous, and unequal. In the female there is nothing but their size to distinguish 

 them, while in the male the internal branch is more delicate in structure, broader, and 

 carries a short, obtuse stylamblys armed with a few cincinnuli. The four following pairs 

 of pleopoda are alike in size and general form, each branch being equally important. In 

 the female the inner one carries a single stylamblys fringed on one side with long hairs, 

 and the male carries two, one fringed with hairs the other tipped with cincinnuli. On 

 all the pleopoda the hairs are abundant, and thickly fringed with long cilia. 



