5920 C. GORDON HEWITT. 
layer of cells is proportionately much thicker. The cortical 
tissue is made up of cells of varying sizes, but which can be 
grouped in two classes—smaller cortical cells and larger 
ganglionic cells. Most of the ganglionic cells appear to be 
unipolar, but there are many of a bipolar and multipolar 
nature present; they stain readily and possess fairly large 
nuclei. These ganglionic cells are arranged segmentally, and 
occur near the origin of the nerves. In the posterior region 
of the ganglion, where the nerves arise in close proximity, the 
ganglion cells are very numerous, relatively few of the cortical 
cells being found. A further demarcation of the component 
ganglia is brought about by median and vertical strands of © 
the ganglionic sheath-tissue, which perforate the compound 
ganghon and occur as vertical strands along its median line. 
Tracheze also penetrate the ganglion with these strands of 
capsular tissue. 
On the dorsal side of the anterior end of the ganglion is 
situated a pair of spherical structures (c. l.), which may be 
termed the “cerebral lobes.’ They are united in the median 
line dorsal to the foramen traversed by the cesophagus (ce.). 
These cerebral lobes are chiefly of an imaginal character, and 
contain the fundaments of the supra-cesophageal ganglia and 
also of the optic ganglia of the future fly (fig. 27). Hach is 
surrounded by a thin membranous sheath (sh.) and is con- 
nected with the major cephalic imaginal discs by the optic 
stalk (0. s.). 
The nerves arising from the ganglion may be divided into 
three groups, according to their origin. lHleven pairs of 
nerves (fig. 24, 1-11) corresponding to the eleven pairs of 
ganglia arise, two from the anterior end and nine from the 
sides of the ganglion. Three pairs of nerves (a., b. and c.) 
arise laterally from the stalis of the pro-thoracic and meso- 
thoracic imaginal discs. In the median dorsal line of the 
posterior half of the ganglion a single pair (d. a.’) and two 
median unpaired (d. a.” d.a.”’) nerves have their origin ; 
these are accessory nerves. 
The first pair of the two anterior pairs of nerves runs 
