14 
THE VOYAGE OF H.M.S. CHALLENGER. 
with a yellowisli-brown coloured mass of a fatty nature. Between the two walls of 
the stomach, nuclei of nearly the same size as those of the connective tissue are visible. 
Nervous System . — The supracesophageal ganglion, also, has nearly kept its original 
position ; it is situated against the oesophagus, a little anteriorly to the place where it 
communicates with the stomach. In PI. I. fig. 2 it is figured in its natural position 
and condition ; in PI. III. fig. 5, and PL I. fig. 4, it is seen in transverse section ; 
numerous rounded ganglionic cells are placed at the periphery, and the whole interior of 
the ganglion is occupied by the medulla. PI. I. fig. 4 distinctly shows the commissures 
which serve to unite the ganglion with the large thoracic ganglion. In the preparation 
which is figured (PI. I. fig. 2) these commissures could not be made out, nor has this been 
possible in any of the other preparations I made by the aid of needles. 
This thoracic ganglion represents alone the whole ventral nerve-cord ; together with 
the thorax, it has changed its place and has been transposed in a direction towards the 
front of the animal, so as to be now attached before the supracesophageal ganglion ; it 
has an elongate oval shape with numerous ganglionic cells at the periphery. In a trans- 
verse section such as that figured (PI. I. fig. 5), we observe that the ganglionic cells form 
a much thicker layer on the side which is directed towards the thorax than on the other 
side ; the lateral symmetry of the ganglion is very distinct, the medulla forming two 
rounded portions which meet in a straight line in the middle of the ganglion. The nerves 
given off from this ganglion as well as those from the supraoesophageal ganglion are 
extremely delicate and are hardly recognisable as such ; two somewhat stronger nerves 
start from the commissures very close to the supraoesophageal ganglion, and a distinct 
nerve is attached terminally to the thoracic ganglion, but as for other nerves, I 
found it impossible to distinguish them with certainty from the fibres of the connective 
tissue. 
There are no organs of sense ; even the sense of touch can be only very slightly 
developed, as the whole body is enclosed within a chitinous bag bearing only chitinous 
spines on its surface. The hairs on the antennae (PI. I. fig. 3) no doubt once per- 
formed the function of organs of touch, but after the antenna has attached itself the 
function of these hairs can no longer be of any importance. Close to the supra- 
oesophageal ganglion I always observed two little bodies, which, from their position, I at 
first felt inclined to consider as belonging to the nervous system. They are kept in 
their places by the connective tissue, and they are situated near the corner between the 
stomach and the supracesophageal ganglion. Their structure is that of an oval bag 
slightly pointed at one or both extremities, lined by an extremely delicate mem- 
brane and filled with a granular substance of a brownish-yellow colour, having 
numerous nuclei scattered throughout its interior (PI. I. fig. 2, gl.). Most probably 
these organs represent the remains of the appendages of the oesophagus (PL II. 
figs. 1, 2, C) of the pedunculated Cirripedia, which are very distinctly developed in the 
