BY W. R. COLLEDGE. 57 
side of the beak for a considerable distance before insertion. 
It is evidently the adductor muscle of the organ. The 
digestive canal commencing in the lower portion of the 
head curves upwards, where it receives the ends of two 
tubes, the hepatic diverticula. Its walls are thick and 
muscular, the central cavity being smaJl in comparison. 
In health it is always undergoing a rhythmic contraction 
and expansion, the movement commencing anteriorly, 
and continuing the whole length of the canal. The lower 
end of this is closed by a strong sphincter muscle, which 
opens into a second oval cavity terminating in the anus. 
The aperture for the ejection of the contents being placed 
at about the fifth tooth of the telson. 
The dark eye is very prominent. It consists of a large 
mass of black pigment, and on each side seven or eight 
lenses are placed on the lateral periphery. In some of 
the English species the lenses are more numerous. The 
organ seems to rest in a large cavity, and is not fixed, for 
it can be rotated to some extent, the motion giving it 
a characteristic tremulous appearance. A bundle of 
muscles and nerves connect it with the brain, and on the 
latter is seen the macula nigra, or eye spot. This is absent 
in some forms. 
One of the most noticeable things about it is the move- 
ment of the heart. It lies near the dorsal line on the 
opposite side, and in a line with the beak. Oval in shape, 
it is quite transparent, and furnished with strong, circular 
and longitudinal muscles. It contracts with great rapidity. 
There are two slits in a transverse direction on the opposite 
sides.. In contracting, these slits are closed, and the blood 
is forced into an arterial vessel, which curves backwards 
to run by the side of the digestive canal. No general 
venous system is traceable, but the blood, which is colour- 
less, can be traced by the particles which float in it. There 
is a canal proceeding from the region of the heart towards 
the lower part of the occiput. Along this the blood flows, 
and passes by a channel formed around the edge of the 
carapace by the juxtaposition of the inner shell. Around 
the eye a broad current flows, freely bathing all the tissues. 
The ovaries or egg sacs lie along the abdominal canal, 
a duct opens from them into the space on the back, called 
