18 
Siphonophora Rosarum 
from above, appears nearly as large as the cerebral ganglion to which it 
belongs. Each cerebral ganglion gives off a nerve to the antenna of its 
side, and a short stout nerve is given off from each optic lobe to the 
eye and ocellus to which it is adjacent. From the lower and smaller 
portion of each of these two cerebral ganglia arises a short circum- 
oesophageal connective, joining them up with the sub-oesophageal 
ganglia, and, through the loop thus formed, the oesophagus passes in its 
course from the mouth. 
From each sub-oesophageal ganglion a nerve is given off which 
passes forward and is lost among the maze of muscles connected with 
the mouth parts. 
Extending from the sub-oesophageal ganglion is an elongated 
portion which, as already suggested, probably represents the anterior 
portion of a primitive double nerve-chain. Joined to this elongated 
portion is the ovoid mass of nervous material mentioned previously as 
being made up of three pairs of thoracic ganglia and a single median 
abdominal ganglion. Each of the paired thoracic ganglia gives off a 
nerve to its respective leg, and each nerve appears to bifurcate just 
previous to its entry into the leg. From the abdominal ganglion a 
Fig. 12. The distribution of the nerves from the thoracic ganglia, and the median 
abdominal ganglion. ( x 54.) 
n. 2nd and 3rd Ig. = nerves to the 2nd and 3rd legs. n. aid. = abdominal nerve. 
n. seg. = nerves to the abdominal segments. n. visc. = nerve to the viscera. 
p. aid. g. = posterior abdominal ganglion. th. g. = thoracic ganglia. 
