SEA-FISHERIES LABORATORY. 409 
In order to inject the venous system the syringe can 
be put into the afferent branchial vessel (fig. 16, Br. af’.). 
Care must be taken that the tissue separating the two 
branchial vessels is not perforated. Further, when 
injecting the venous system, the valves must not be 
removed, but the convex valve should be broken away 
varetully, piece by piece, with bone forceps, right up to 
the attachment of the adductor muscle to the shell. The 
muscle must not be separated from the valves, for a large 
sinus will be otherwise broken into. If the oil mixture 
is used for both these injections the course of many of 
the main vessels can be followed, but it is not permanent 
and will not allow of the dissection of arteries and veins 
in the visceral mass and other deep-lying parts of the 
body. For this latter purpose, ordinary table jelly 
coloured with carmine, and melted with juste ay lila 
water, proved quite satisfactory. It is necessary, previous 
to injecting with the hot jelly, to place the specimen in 
warm water for about half an hour. 
ARTERIAL System (fig. 14). 
The blood leaves the ventricle by two main vessels, 
the anterior and posterior aortae. 
The Anterior Aorta (figs. 14 and 19, Ao. ant.) is a 
large artery which arises from the ventricle at the middle 
of its dorso-anterior edge above the alimentary canal, and 
passes forwards directly over the latter to the digestive 
gland. There is an aortic dilation just after leaving the 
ventricle, inside the pericardium, and this can be seen to 
expand after each contraction of the ventricle. 
On reaching the posterior end of the digestive gland 
the aorta passes dorsally along its middle line, giving off 
a small vessel on each side (figs. 14 and 19, a.) which pass 
