]3() THE VOYAGE OF H.M.S. CHALLENGER. 



densely sen-ate aspect. What the real function of this peculiarly modified pair of legs 

 U, I am wholly unable to state. Meanwhile, we have every reason to assume that 

 so remarkable a structnre cannot but stand in close connection with some unknown 

 requirement bearing on the vital phenomena of the animal. 



The four succeeding pairs of legs (figs. 16-20) are comparatively very short and 

 somewhat clumsy in structure, with the joints slightly compressed and fringed along the 

 inner edge with slender bristles. Of the joints, the ischial and meral are the largest, and 

 nearlv equal in length. The terminal part, comprising the three outer joints, is 

 remarkably short, not nearly attaining the length of the meral joint, and exhibits 

 several strong spiniform bristles, six to eight of which issue from the very small terminal 

 joint (fig. 17). 



The penultimate pair of legs (figs. 21, 22) are exceedingly small, and almost hidden 

 between the gills, but have l)oth the endopod and exopod distinctly defined. The 

 former consists, as in Thysanoessa, of only two joints, the terminal the longer, both with 

 a few scattered bristles along their inner edge. 



The last pair of legs (fig. 22, 23) are cjuite rudimentary, each forming merely a small 

 laminar plate, originating from a short basal part. This plate, whicli undoubtedly 

 represents the exopod, is somewliat unlike that in Thysanoessa, being ratlier expanded 

 and liroadly truncate at the apex, which, together with the inner edge, is fringed with a 

 dense row of ciliated bristles. 



The gills are rather fully developed, forming a broad fringe beneath the carapace 

 along the sides of the trunk (see PI. XXIII. fig. 10), and, as usual, increasing successively 

 in size from before backwards. The two anterior pairs (PL XXIV. figs. 13, 16, 24) 

 exhibit much the same appearance as in Thysanoessa, constituting, as they do, single 

 stems, expanded at the apex into two recurving corners, and with a regular series of 

 digitiform gill-lobules along the posterior edge. The four succeeding pairs (figs. 25-28), 

 on the other hand, are all of them double, or exhibit two distinctly defined stems, the 

 outer of which corresponds perfectly in structure with the two anterior pairs of gills, 

 whereas the inner stem is bent inward, exhibiting a somewhat pyramidal form, and 

 furnished at both edges with a clustering assemblage of gill-lobules. This stem, too, is 

 not, as in Tliysanoessa, connected with the outer one, but would seem to spring- 

 separately from the coxal joint of the leg, becoming, as usual, gradually more complex 

 posteriorly. The last pair of gills (fig. 29) are very large and complex in structure, 

 consisting of two principal portions that point in opposite directions, both, but especially 

 the outer one, being richly arborescent. 



The pleopoda of the female do not exhibit any marked peculiarities ; those of the 

 male I had no opportunity of examining, the collection containing female specimens 

 only. 



The telson (see fig. 30) is very slender and elongate, attaining nearly the length of 



