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



ventrally (fig. 12). Of the several divisions of the hody which are distinguished in the 

 adult animal, the anterior or cephalic part is, as above stated, very massive and about as 

 long as the succeeding division or trunk, which exhibits, within the larval cuticle, all 

 its segments well defined. The posterior part of the body, on the other hand, including 

 the pleon and the tail, is still rather imperfectly developed and scarcely longer than 

 the trunk. It consists of only five segments besides the caudal rami, and if the four 

 anterior of these segments be referred to the pleon, the tail will then only be represented 

 by a single segment. The free edges of the developing carapace (fig. 12, C) can easily be 

 traced on each side as a curved line extending backwards from the base of the eyes and 

 meeting above at the most anterior part of the trunk. The carapace is thus in this 

 stage chiefly confined to the cephalic part, the greater portion of the trunk being exposed 

 behind it. The rostral plate (R) is also readily detected as an obtuse protuberance 

 curving interiorly in front and not yet marked off from the carapace. The several 

 appendages belonging to the cephalic division are all visible, though still rather 

 imperfectly developed. The eyes (0) constitute two rather large recurved prominences, 

 which, however, as yet show no trace of either pigment or visual elements, and are also 

 quite smooth, not as in the adult animal denticulate. The antennulse (a 1 ) and antennas 

 (a 2 ) are of a very similar appearance, forming simple digitiform recurved processes 

 projecting freely from beneath the anterior part of the head, the former slightly diverging 

 the latter extending straight backwards along the ventral surface. Between the base of 

 the antennas a rounded prominence (L), still invested by the larval cuticle, is seen, 

 representing the anterior lip. Somewhat posterior to this prominence, three pairs of 

 rather small and closely crowded processes occur, the two anterior pairs exhibiting a 

 slender terminal appendage, distinctly marked off from the proximal part, and somewhat 

 recurved. Of these processes the anterior pair (M) represent the mandibles, and their 

 terminal appendage the mandibular palp; the succeeding pair (m 1 ) are the first pair of 

 maxillas, and their terminal appendage, which is considerably narrower than that of the 

 preceding pair, is easily recognised as the slender recurved palp of these maxillae; the 

 third pair (m 2 ), finally, are as yet quite simple, conical in form and represent the second 

 pair of maxillae. On each of the eight segments of the trunk there are a pair of 

 bilobular appendages (brp) pointing posteriorly and each partly covering the one succeed- 

 ing it. These appendages represent the developing branchial legs and are all exactly alike 

 and slightly extended laterally. They are succeeded by three pairs of appendages (pi), 

 which are also distinctly bilobular at the tip, but much smaller and quite concealed by 

 the larval cuticle. These appendages are the three anterior pairs of pleopoda. No 

 trace can as yet be detected of either member of the fourth pair of pleopoda, or of the 

 two succeeding pairs of rudimentary caudal lirabs. The caudal rami (ur) form simple 

 obtusely conical processes, lying within the symmetrically formed bilobular extremity of 

 the larval cuticle and being well defined from the last segment, but as yet without any 



