STUDIES ON THE NERVOUS SYSTEM OF ORUSTACEA. 49 
other backwards along the ganglionic cord. Numerous ele- 
ments of this kind have stained in embryos near the point of 
hatching, and it has been possible to trace the fibres inside 
the central nervous system for considerably greater distances 
than was done before. 
In the thorax, elements having the characteristic Y-shaped 
bifurcation enter the various ganglia by the posterior roots. 
One such fibre is represented in fig. 1 at M, Th. x. From this 
ganglion (Th. x) it has been traced forwards by direct ob- 
servations as far as Th. 1, but there was no indication of a 
definite ending there, the blue colour becoming gradually less 
distinct and suggesting that the true termination had not been 
reached.! From Th. x1 the element has also been traced as 
far as Th. 1. 
In the abdomen, elements of this kind enter by the middle 
root of the three which belong to each ganglion. From Abd. 
1 the forward branch has been actually traced as far as Th. 11, 
but gave no indication of a definite ending there. 
From the three ganglia already mentioned the forward fibre 
has been directly observed to pass through at least nine or ten 
ganglia. Cases in which the fibre could be traced from these 
and neighbouring ganglia through five, six, and seven ganglia 
occurred in a large proportion of the numerous preparations of 
late embryos that were made. The fibres from spindle-shaped 
cells lying in the telson can, in embryos of moderate age, be 
seen to enter the last abdominal ganglion and then to run 
forward through the anterior ganglia. Such fibres have been 
traced as far as Abd. 1, but could not be followed further on 
account of the flexure of the abdomen. 
The fact mentioned in Part I, that elements of the kind 
1 If an element stains at all frequently it is generally possible to form an 
opinion as to whether the actual termination has been reached, or whether 
the staining is incomplete. In the former case the terminal portion is, gene- 
rally, at least as deeply stained as any other part of the element, and it may 
continue to take on a stronger colour after there has been a considerable 
fading of the other parts. In the case of incomplete staining, on the other 
hand, the colour becomes more and more faint towards the end of the fibre 
until it finally disappears. 
VoL. 39, PART 1.—NEW SER. D 
