STETJCTUEE AND BIOLOGY OP SCHIZONBTJEA LANIGEEA. 683 
which occupy the greater part of the head ; a pair of fused sub- 
oesophageal ganglia ; and an elongate median ganglion, lying 
in the thorax beneath the oesophagus. The latter represents 
the fused elements of the ventral nerve chain, and comprises 
the three fused thoracic ganglia, to which the sub-oesophageal 
g’anglia are attached by two broad commissures, and a median 
abdominal ganglion. Nerves are given off from the ganglia 
to the appendages and other parts of the body. 
The supra-oesophageal ganglia occupy the epicranial region 
of the head. They consist of two fused, pear-shaped ganglia, 
which have their widest part towards the anterior or dorsal 
wall of the head (figs. 18, 21). Histologically they consist of 
an outer coat of ganglionic cells with deeply staining nuclei, 
and an inner, lightly stained area composed of an interlacing 
mass of nerve fibres. 
Near the infra-posterior end of these ganglia, two short 
circum-cesophageal commissures (cs.) lead round the oeso- 
phagus, and connect with the sub-oesophageal ganglion, 
forming a loop through which the oesophagus passes. 
From the antero-dorsal end of the supra-oesophageal 
ganglia a pair of antennal nerves (?i. a. fig. 21) are given off 
laterally to the antenna), behind which are a pair of small 
nerves which pass to the eyes. 
The sub-oesophageal ganglion (sh. g.) is smaller, and is con- 
nected wdth the thoracic ganglia by means of two broad com- 
missures. From its anterior end a pair of small nerves arise, 
which innervate the proboscis, and another pair innervate the 
maxillae and mandibles. 
The fused thoracic ganglia, together with the median abdo- 
minal ganglion (a. g.), form an ovoid, elongate mass, wliich 
extends in the median line along the ventral surface of the 
thorax. 
The histological structure of these ganglia is the same as 
before, consisting of an outer coat of ganglionic cells possess- 
ing nuclei of varying sizes, and an inner, whitish-grey, 
medullary region, composed of an interlacing network of 
nerve-fibres. 
