158 



Part III. — Twenty-first Annual Report 



they are not exactly opposite one another. The telson exemplifies 

 Mayer's typical number of spines — 14. 



The anus opens on the ventral surface of the telson (an, Fig. 157). 

 The end of the gut issues through a round aperture {op) in the integu- 

 ment. 



II. Abdomen, Pleopods (Fig. 124). The only noticeable feature of 

 the abdomen in this stage is the larger size of the rudiments of the 

 pleopods (pi). They are still single. 



Telson (Fig. 119). The telson is rather longer and slightly , 

 narrower in proportion. On each leg of the furca one tooth only was 

 made out. 



III. Abdomen (Fig. 117). The joints of the abdomen retain the 

 characters of the I. Zoea. Another joint has, however, been added to 

 the abdomen by the segmenting ofi' of the proximal part of the telson, 

 which now forms the sixth abdominal joint {6, Fig. 121). 



Pleopods {ih). The pleopods now project from the hind ventral 

 part of the joint, not apparently through the integument, but issuing 

 between the hind border of the one segment and the beginning of the 

 next. They are paired, and are little conical protuberances which in 

 some cases show a faint line of segmentation off from the abdominal 

 joint. The pleopod of the new or sixth segment does not project 

 externally. The projecting pleopod buds belong to the second, third, 

 fourth, and fifth segments. 



Telson (Fig. 121). The telson is much shorter comparatively than 

 in the previous stage, owing to the separation just in front of the anus 

 of the last abdominal joint, otherwise it has not changed from II. 

 Zoea. Two small hairs were, however, seen on each furcal leg. The 

 anus opens on the telson. 



lY. Abdomen (Fig. 129). The backward-directed portions of the 

 lateral integument of certain of the joints is more pointed than 

 rounded. 



Pleopods {ih). The four pairs of pleopods of the last stage are now 

 long spatulate processes. The pleopods of the sixth abdominal seg- 

 ment appear as small processes {ih), and 5 Fig. 137. They are 

 more widely separated from one another than are the individuals of 

 the other pairs. 



Telson (Fig. 137). The tooth on the furcal leg is reduced to very 

 small proportions. The serrated spines on either side of the furcal 

 angle have remained unchanged during the Zoea stages. 



Megalops. The Abdomen (Figs. 138 and 143) has approached 

 nearly to the adult form. It remains extended (Fig. 152), however, 

 and is never tucked in under the thorax. A few short plain hairs are 

 found on its dorsal surface ; a pair of these is found on the dorsum of 

 each segment except the first and sixth, a pair is situated on the 

 hind inferior corner, and a varying number along the hind dorsal edge 

 of each segment. 



The Telson (Figs. 143, 127, a and h) is rounded, with its hind 

 border a little flattened. On its dorsal surface there is a pair of short 

 hairs. On the ventral surface the anus opens. 



The Pleopods (Fig. 138) are five pairs, attached to the second, 

 third, fourth, fifth, and sixth segments of the abdomen. The first four 

 pairs are similar to one another ; chey are biramous, the exopodite 

 being large and spatulate in shape, the endopodite a short oval process. 

 The fifth pair of pleopods, which arises from the hind ventral region 

 of the sixth segment, are 1 -branched and very much smaller than the 

 preceding pleopods (Fig. 127, a). 



The pleopods are the swimming organs of the Megalops, and each 

 exopodite of the first four, and the single-branched fifth, are provided 



