of the Fishery Board for Scotland. 145 
middle: a joint was not satisfactorily made out. A swelling has 
appeared on its distal half. This is the rudiment of the single-jointed 
process of the Megalops. The ganglion is in the distal half of the joint. 
Mecators (Fig. 29). The antennule is now a very different organ. 
It is 2-branched. The first joint of the appendage in the I. Zoéa 
is no longer to be made out; it has probably fused with the cephalon, 
The antennule consists of seven joints, a large basal joint, triangular in 
shape, representing the broad proximal half of the appendage in IV, 
Zoéa, and six other joints which represent the distal half of the long 
joint in IV. The second and third joints are broad, and contain within 
them the ganglion, now divided into two. The third joint has a broad 
distal end, from the projecting corner of which a single-jointed 
appendage arises. The latter joint is tapered, constricted at its middle, 
and bears four terminal smooth hairs; and two other shorter hairs arise 
from the joint as shown in the figure. It is the endopodita. 
Distal to the third broad joint there are four narrower joints: the 
fourth, fifth, and sixth are short, the seventh a long joint constricted 
at its middle. There are three main groups of aesthetascs attached to 
the last three joints. On the fifth joint there are three; on the sixth, 
five (in one case four); and on the seventh a group of three about the 
middle of the joint, and a single one a little short of the end of the 
joint. On the end of the joint there is a long sparsely ciliated hair. 
There are several short hairs distributed over the other joints: these 
are shown in the sketch. 
The first joint contains the auditory organ, for a minute description 
of which see Hensen’s* and Prentiss’f papers. 
The sensory tubes are connected by tubes with the ganglion, which is 
not single but composed of different ganglia, which appear to serve 
different aesthetascs or groups of aesthetascs. The compound ganglion is 
situated in the second and third joints. From the position of the 
ganglion we are able to homologate the different portions of the 
antennule of the Megalops with that of the IV. Zoéa. The lower half 
of the long pear-shaped joint becomes the first joint of the Megalops ; 
and the remaining six joints and the short appendage from the third 
joint are derived from the distal half of IV. The little 1-jointed 
appendage is the endopodite: the aesthetase-bearing appendage is the 
exopodite. 
In Carcinus we have an exactly similar condition to what is found in 
Crangon vulgaris.£ In the latter the auditory organ is in the first joint ; 
the compound ganglion is located in the second and third joints, and 
from the the third joint arise an exopodite [3-jointed] bearing groups 
of aesthetascs, and an endopodite [2-jointed] bearing hairs only. In 
Crangon, however, the antennule in the VI. stage (Megalops) is straight, 
whereas in Carcinus the antennule is bent over on itself. 
1. (Figs. 18, 20,21.) In the first young stage the condition is practi- 
eally identical with that of the Megalops, except that with increase in 
size the joints are more numerous. The first three joints are unchanged, 
except in size, but the terminal joint of the exopodite is now segmented, 
and the l-jointed endopodite is now 2-jointed. That is, the antennule has 
now eight joints, with a 2-jointed endopodite rising from the third 
joint. The endopodite and exopodite are bent down towards the third 
joint. ; 
Zoolena Bd Peer ct het ey re der Decapoden,” Zeitschr. f. wissenschaft, 
+ Prentiss, “‘The Otocyst of Decapod Crustacea: its Structure, Development, and 
Functions,” Bull. Mus. Comoar Zoology, Harvard vol. xxxvi., No, 7, 10 pl. Cambridge, 
U.S., A., 1901. 
£ Op. cit. 
