144 Part L11.—Twenty-first Annual Report 
The number of aesthetascs was found to be—four in the proximal 
group, four in the next, three in the distal, and beyond that group a 
single aesthetasc arose from the middle of the end joint. 
The exopodite bears a long smooth terminal hair. 
A few minute “ needle-point” cilia were found on the second joint. 
Antenna, A., Pl. vii. 
I, (Fig. 16). The antenna of the I. Zoéa consists of a single basal 
joint which is produced distally into a long spine, serrated on both sides 
(Fig. 1, 6). At the distal end of the joint there articulates a branch 
consisting of a long narrow joint which bears two smooth spines, one 
very long, the other short. The distal end of the long joint is serrated 
(Fig. 1, @), and the short spine rises from a projecting corner of the 
same. This branch is the exopodite, and it is the homologue of the 
scale of the antenna of Crangon vulgaris. It is present in the Zoéa, 
but absent in the adult. 
The serrated process is the endopodite, and from it is developed the 
flagellum, z.e. the antenna of the adult. On the proximal part of the 
process there is a swelling (sw, Fig. 16), which is the rudiment of the 
flagellum. During the succeeding Zoéa stages it grows in size along- 
side but quite independently of the serrated process. In this respect 
Carcinus differs from Crangon. In the latter the serrated process 
develops into the flagellum. The future whip first appears in the wide 
proximal part of the process, and as it grows it absorbs the serrated 
portion till the latter becomes merely a tuft of hairs on the end of the 
former. In Carcinus, however, in the IV. or last Zoéa stage the 
serrated process is as large and important proportionally as in the I. 
Zoéa. 
The serrated process in both forms is a character of the Zoéa alone. 
During the succeeding Zoéa stages, development in the antenna takes 
place only in the bud of the flagellum, the other parts remain unchanged 
in form, though they increase in size. 
IT. (Fig. 17). The rudimentary flagellum is now prominent as a 
conical protuberance. 
TIL. (Figs. 4, 5). The flagellum is now half the length of the serrated 
process. 
IV. (Fig. 6). The flagellum is now almost as long as the serrated 
process. The exopodite has diminished in relative size. 
Meeators (Fig. 11). The antenna now has its adult form. It 
consists of nine joints, the first three are wider than those that follow. 
The latter, with one exception, viz. the fourth joint of the antenna, are 
long narrow tapering joints. The antenna is furnished with two 
prominent long smooth stiff hairs. They arise from the distal end of 
the seventh joint. With them are associated two short hairs. The 
terminal joint bears three stiff smooth slender hairs, and round the 
distal edge of the fifth joint there is a ring of four short hairs. On the 
third joint there is one short hair, and on the first joint there are three 
similar hairs. In another Megalops the antenna had only eight joints, 
the fifth and sixth joints of the form drawn being fused together. The 
first joint of the antenna appears to be the protopodite, and is probably 
the homologue of the basal joint of the antenna of the Zoéa. 
1. (Figs. 7,21, and 23). In the first young stage there is little change 
from the condition in the Megalops. Considerable variation was found 
in the antenne of different individuals. In one (Fig. 7) there were 
ten joints; the arrangement of hairs was practically the same, except 
that a joint seemed to have been added to the first three joints, so that 
