STUDIES ON THE NERVOUS SYSTEM OF ORUSTACEA. 471 
and then forwards and inwards, gives off a branch to the 
neuropile of the same side, and then passes across to the other 
side. It runs forwards to the brain along the outer border of 
the neuropile, and breaks up at a point nearly as far forwards 
as the terminations of Th. V and VIII, but somewhat lateral 
to them. 
No collateral branches have been observed in ganglia other 
than that in which the element originates. 
C. 
These elements are best observed in the posterior ganglia of 
the thorax of very late embryos or young larve. Their exist- 
ence in practically the same condition can, however, be made 
out very much earlier, in fact soon after the eye-pigment begins 
to deposit. They are represented in fig. 4 in red, whilst fig. 7 is 
a drawing of one of these elements made from a fresh prepara- 
tion. Several of them are also shown in fig. 8, which is drawn 
directly from a preparation fixed in ammonium picrate. 
These elements have been clearly demonstrated in each seg- 
ment between Th. VI and Th. XI, and there is evidence of their 
existence in the more anterior segments. Starting from a cell 
in the anterior portion of the lateral mass of ganglion cells, the 
fibre passes inwards and backwards for a short distance, and 
then turns till it runs almost directly backwards, giving off to 
the neuropile numerous branches, which are themselves 
arborescent. After a short backward course it again turns in- 
wards, and finally runs directly backwards between the fibre of 
series D (blue in fig. 4) and the median ganglionic mass. 
Each element ends in a tuft of fibres (figs. 4 and 7), which lies 
at the posterior end of the ganglion next to that in which the 
element originates, and immediately opposite the terminal 
tuft of one of the D elements. 
D: 
These elements are also best observed in very late embryos. 
They appear to be intimately associated with those of group C, 
and generally stain in the same preparations. They are repre- 
