218 ANNULATA., 
paired hepatic arteries. Posteriorly the heart gives off a 
dorsal abdominal backwards, and a sterna/ artery down- 
wards which, on reaching the ventral surface, divides 
into a ventral thoracic forwards and an abdominal back- 
wards. 
All these arteries supply the organs with pure blood, 
and the impure venous blood accumulates in the cavity of 
the body whence it passes out to each gill by an afferent 
branchial. After zxration in the gills, it is collected by 
efferent branchials and passed by branchio.cardiac canals up 
the sides of the thorax into the pericardial sinus. 
The heart of the lobster is thus sys¢emzc, and the course 
of the blood is as follows :— 
Hearl 
Arferial body eavily 
~ 
\pericerdial 
System Gills *"°"* 
Venous body cavny 
The special point to notice is the hemoccelic body- 
cavity converting the venous system into a number of large 
sinuses or spaces, the arterial vessels alone having definite 
walls. 
The nervous system is constructed on essentially the same 
plan as that of the Annelida, but there are more concentra- 
tions of the ganglia. If the lobster were a simple 
annelid we might expect to find a dorsal brain 
over the anterior end of the alimentary canal, a ring round 
it to the ventral surface, and a double nerve-chain to the 
hind end, with double ganglia in each segment; but in reality 
matters are rather different. The Jrvazm of the lobster has 
the true brain portion supplying sensory nerves to the eyes, 
but, in addition, it has the two next pairs of ganglia belonging 
to the antennules and antenne fused with it. The-anten- 
nules and antenne are really post-oral appendages, but they 
move forward in development to the adult position in front 
Nervous. 
