408 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
upon the floor of the pericardium (fig. 18, Aur. C.). The 
heart beat is slow, an average of about twenty-five to 
thirty contractions per minute. It is necessary to inject 
the blood system to follow its course, and owing to the 
fact that the digestive gland is of a very dark colour, 
whilst the visceral mass is, on the other hand, of a light 
tint, injections must be made with both light and dark 
colours, in order to determine the course of the blood 
vessels in all parts of the body. 
A great part of the vascular system can be made out 
by using an injection mass formed of a mixture of lard, 
linseed oil, and yellow oil paint (chrome vellow, as sold 
in collapsible tubes, will do very well), in such a 
consistency that it will run fairly easy (a little less 
viscous than glycerine). Care must be taken not to have 
any solid particles left in the coloured mass. It is 
necessarv to prepare the specimens, for it is useless 
attempting to inject the living animal since the 
contraction of the muscles closes up the vessels. The 
necessary state of muscular relaxation can be produced by 
placing the animals in a bucket of sea water and adding 
slowly, at intervals, to the surface some of the following 
mixture :—-100 c.c. 75 per cent. alcohol, 100 c.c. glycerine, 
and 200 c.c. sea water. In about eighteen to twenty-four 
hours, the specimens were narcotised and could be 
transferred to formalin (5 per cent. solution) for about 
half an hour without further contraction; they were then 
ready for injection. For the arterial system, the best 
point of attack was found to be the efferent branchial 
vessel (fig. 16, Br. eff.), in the ctenidial axis, with the 
point of the syringe directed towards the heart. This 
will inject the anterior and posterior aortae, the adductor 
artery, and in fact the whole of the arterial. system, 
together with the mantle or pallial vein, 
