4.70 EDGAR J. ALLEN. 
B Th. I1.—The cell lies in the ventral median mass of ganglion 
cells. The fibre runs forwards and outwards, and then decus- 
sates. After reaching the opposite side it goes forwards to the 
brain. It has been traced as far as the cross in the figure. 
No collaterals have been observed after the fibre leaves Th. I. 
A similar element occurs on the opposite side. 
B Th. II.—Cell lies in lateral mass. Fibre gives off a large 
arborescent branch in Th. II, and one also which passes down- 
wards to Th. III. It then runs across to the opposite side, 
turns forwards, and goes to the brain. No collaterals have 
been observed, with the exception of those figured. 
This element generally forms a conspicuous object when 
stained, on account of the comparative stoutness of the fibre at 
the part where the branches occur, and the richness of the 
arborescence. 
B Th. Vi —These elements will be considered together, 
Bi Th. Wall, as they appear to be very intimately associ- 
ated, ending in the same part of the brain, and being generally 
found stained in the same preparations. The cell of each 
element lies in the anterior portion of the lateral ganglionic 
mass. Soon after entering the neuropile the fibre gives off 
two branches, one running forwards and breaking up in the 
hinder portion of the ganglion immediately anterior, whilst 
the other runs backwards and breaks up in that immediately 
posterior. The main fibre turns inwards, crosses its fellow of 
the opposite side, and then bends forwards, running close to 
the median ganglionic cells, until it enters the brain. In the 
brain the fibre continues to run forwards, giving off many 
branches, and ends at about the level of the nauplius eye. 
These fibres have not been observed to give off collaterals 
during their course through the thorax. 
The two pairs of elements just described very frequently stain 
with methylene blue, and the characteristic figures produced by 
their decussation are very useful landmarks in preparations. 
B Th. VI.—This element resembles B Th. I more nearly than 
B Th. II, V,or VIII. The cell liesin the ventral median mass 
of ganglion cells. ‘The fibre curves outwards and backwards, 
