82 Part 11. —Twenty-third Annual Report 
with the pleopods of the megalops. The telson of the “IV.” stage, 
which was drawn, had no median spine on the hind border ; in this 
stage a median spine is usually present. 
Stage “IV.” attracts attention from the fact that in general shape and 
large size it resembles a megalops. The use of the pleopods for 
swimming give it the characteristic megalops appearance. It swims 
with the chele stretched straight out in front of it. It may be 
regarded either as a backward megalops, or as a precociously developed 
zoéa. From the point of view of the former, the antenne, which are so 
prominently employed by the megalops, have developed more slowly 
than the pleopods, We have, in fact, a megalops which has carried over 
certain zoéa characters, viz. antennules, antennz, the purely maxillipede 
form of the pereiopods, and the abdominal hooks. There are other cases 
in which minor zoéa characters are carried over and exhibited in the 
megalops; they will be referred to later. If the second view is adopted, 
we are led to the interesting conclusion that an organ may by precocious 
development become functional in a stage which is normally withont it. 
Might not an unusually rapid growth of the zoéa in size necessitate the 
earlier provision of swimming organs to assist the exopodites which were 
sufficient in the smaller stages? Or might a lower salinity react by 
stimulating the development of greater swimming power? The zoéa has 
attained to the body of a megalops, and the result is the provision of the 
means of moving it about. 
Boas describes considerable difference in structure between the larvee 
and adults of the fresh-water and sea-water forms of Palaemonetes 
varians. The larva of the former is larger than that of the latter. 
The megalops stage is illustrated by several figures. Fig. 72, pl. iv.. 
shows the lobster in this stage. The pereiopods are represented by figs, 
60, 61, 62, and 58, pl. iii., while the abdomen and telson are shown in 
figs. 57 and 63, pl. iii. 
The exopodites of the pereiopods are present, and setose, though very 
much reduced ; but variations in the exopodites are common. In the 
stage following the megalops, viz. the first young stage, the exopodites 
are reduced to little processes (vide figs. 59, 65, 70, pl. iv.). 
While dissecting a megalops the first pereiopods broke off at the 
junction between the basipodite and the ischiopodite. These joints, so 
far as could be made out, were fixed, as they are in the adult. This is 
the fracture plane of Fredericq. The broken limb showed a clean but 
not very regular break (fig. 58, pl. iii.). The muscles in the ischiopodite 
run right down and terminate at the proximal end of that segment. The 
muscles of the exopodite may have something to do in effecting the 
fracture. 
The pleopods are similar to those of Stage “IV.” (fig. 51, pl. ii.). The 
setee have long, stiff cila, and resemble generally the setz on the pleopod 
of the megalops of Crangon vulgaris. 
The telson of the megalops had a median spine on the hind border. 
This spine is usually absent ; it is a zoéa character. 
The chela resembles that of the first young stage (fig. 65), but the 
tubercles on the meropodite are a little less prominent. 
The first young stage resembles much the megalops (vide fig. 70, pl. iv.), 
but is usually larger. The exopodites of the thoracic limbs are small 
processes, no longer setose. The antennz are longer than in the megalops. 
The pleopods are similar to those of the megalops. The rostrum is 
bifurcate. On the whole, the lobster in the first young stage resembles 
much in its habits the lobster in the megalops stage. It does not appear 
to swim quite so much. 
The first pereiopod of this stage is figured in figs. 65 and 59, pl. ili 
