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



the two brauclies, originally nearly similar in structure^ the outer has assumed the 

 character of an oval scale, fringed along its inner edge and apex with a, regular series of 

 slender bristles, whereas the inner branch has retained its cylindrical furm, though some- 

 what produced and divided into a biarticulate peduncle, and a non-articulate, naked, 

 and digitiform, terminal part, forming together the flagellum. 



In the next Cyrtopia stage the flagellum becomes still more produced. But not till 

 the first post-larval stage does it assume (fig. 8) its definitive structure, the peduncle being 

 then triarticulate, and the terminal part subdivided into a number of distinctl}' defined 

 short articulations, furnished with minute l_)ristles. 



The Mandibles (figs. 10-12). — Also these organs exhibit no change whatever through 

 most of the larval stages, retaining (fig. 10) the peculiar armature of their cutting edges, 

 as described above in the larvae of Nyctiphanes, and also the spiniform projection 

 occurring at the base of the masticatory part auteriorl)'. Of a palp no trace whatever 

 can be detected previous to the Cyrtopia stages, wdien a very small and soft kuob-like 

 projection first appears on the outer fiice of the mandibles, at the l:»ase of the masticatory 

 part. This process becomes, in the second Cyrtopia stage, somewhat more elongate 

 (see fig. 11), but is still non-articulate and naked. Finally, in the first post-larval stage, 

 the palp (see fig. 12) has become considerably jiroduced, and divided into three distinct 

 articulations, the two outer of which bear each a single bristle. In this and the two 

 i:)receding stages, moreover, the peculiar supplementary plate of the cutting edge, described 

 above in the larvae oi Nyctiphanes, and also occurring in the larvro of Euphausia, would 

 ap)pear to be entirely lost. 



The First Pair of MaxiUce (figs. 13-15). — The appearance of these maxilhB in the 

 larvai previous to the Cyrtopia stages (fig. 13) is much the same as that descril)ed above 

 in the larvae of Nyctiphanes, with this exception, however, that the palp is distinctl}' 

 biarticulate. In the Cyi'topia stages, however, the palp becomes uniarticulate, its two 

 original joints being fused together (see fig. 14), and at the same time it assumes a 

 somewhat oval form, still more pronounced in the following stage — the first post-larval 

 (see fig. 15). In the latter stage, too, the true exognath makes its appearance, 

 originating, apart from the larval exognath, in the form of a thin elliptical lamella l^earing 

 only a single bristle at the tip. The larval exognath, with its four strong setas, is still 

 found in this stage beneath the newly formed lamellar exognath, but in the following 

 entirely disappears. 



The Second Pair of Maxilla (figs. lG-18). — Also these maxillae exhibit scarcely any 

 change throughout the true larval stages, their structure (fig. 16) being very similar to 

 that described above in the larvae of Nyctiphanes. The first perceptible alteration is 

 observed in the last Cyrtopia stage, when a new setae has developed behind that 

 affixed to the end of the basal part exteriorly (see fig. 17). In the succeeding stage 

 (first post-larval) three more setae are added (see fig. 18), constituting, along with the two 



