88 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
There are seven pairs of thoracic ganglia (th. g.), the 
ganglia of each pair being closely connected. The pairs 
of ganglia are connected by commissures, those between 
the sixth and seventh pairs of ganglia being very 
short. Hach pair of thoracic gangla gives off a pair of 
stout nerves, which split into several parts, and supply the 
appendages. From the middle of the length of the 
commissures connecting the ganglia, nerves arise which 
innervate the muscles of the body. 
In Ligea the abdominal ganglia are all fused into a 
single ganglionic mass (ab. g.) situated in the anterior 
region of the abdomen. In the Isopoda all stages are 
found, from the original separate condition of the 
abdominal ganglia to the fused condition occurring in 
Ligia. From the abdominal ganglion nerves arise, which 
supply the appendages and muscles of the abdomen; a 
large pair of nerves run from the posterior end of the 
ganglion to supply the uropoda. 
A small median nerve runs between the commissures 
connecting the thoracic ganglia from the sub-oesophageal 
ganglion to the seventh pair of thoracic gangha. It has 
been termed the ‘sympathetic’ nerve, but there is no 
evidence that it is of such a nature. 
SENSORY ORGANS. 
The eyes.—As the eyes of the Ligia oceanica are 
different from the eyes of other Isopods, which have been 
described by Parker, Beddard and others, their structure 
will be given in detail. 
They are compound and sessile, occupying almost the 
whole of the lateral region of the head. In the mature 
animal each eye consists of upwards of 500 ommatidia. 
The corneal cuticula is facetted. The corneal facets of the 
