158 Part IIT —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. AppomEN, PLEopops (Fig. 124). The only noticeable feature of 
the abdomen in this stage is the larger size of the rudiments of the 
pleopods (pl). They are still single. 
Tetson (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. Aspomen (Fig. 117). The joints of the abdomen retain the 
characters of the I. Zoéa. Another joint has, however, been added to 
the abdomen by the segmenting off of the proximal part of the telson, 
which now forms the sixth abdominal joint (6, Fig. 121). 
Preopops (ib). 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. 
Trxson (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. 
Zoéa. Two small hairs were, however, seen on each furcal leg. The 
anus opens on the telson. 
IV. Aspomen (Fig. 129). The backward-directed portions of the 
lateral integument of certain of the joints is more pointed than 
rounded. 
Prieopops (ib). 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 (tb), and 5 pl, Fig. 137. They are 
more widely separated from one another than are the individuals of 
the other pairs. 
Tretson (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 Zoéa stages. 
Mecators. The Aspomen (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. 
Tue Tetson (Figs. 143, 127, @ and 6) 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. 
Tur Pieoprops (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; they 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, «). 
The pleopods are the swimming organs of the Megalops, and each 
exopodite of the first four, and the single-branched fifth, are provided 
