STUDIES ON THE NERVOUS SYSTEM OF CRUSTACEA. 473 
Fig. 1 contains types of most of the elements of this kind 
which have stained. In this figure the general course of the 
nerves springing from the ganglionic cord is indicated. In the 
more posterior ganglia (Th. [V—VIII) it will be observed that 
two nerve-roots exist, one anterior (ant. n. 7.) and one posterior 
(post. n. r.). Fibres passing out at the anterior root go for the 
most part to the limbs, whilst those passing out at the posterior 
root supply the wall of the body, and their general distribution 
is indicated. The anterior root is in reality a double root, the 
two halves separating at a later stage. In Th. II and III this 
separation has already taken place. In fig. 1, for the sake of 
clearness, those elements which originate in cells of the central 
ganglionic mass are coloured red, whilst those having their 
origin in the lateral mass are blue. Each of the ganglia Th. VI 
to Th. IX contains exactly similar elements. One element of 
each kind which has stained has been drawn upon both sides 
in Th. VIII, whilst to render them clearer only one element 
of each colour has been inserted in Th. VI, VII, and IX. 
The lettering will be continuous with that of the elements 
already described. 
E. Type: the Blue Element of fig. 1 in Th. VI 
and VII. 
This element starts from a cell in the anterior portion of the 
lateral mass of cells. The fibre runs first inwards, and then 
curves downwards and outwards, leaving the cord by the ante- 
rior nerve-root. The fibre gives off three main branches to the 
neuropile, which gives a very characteristic trident shape to 
this portion of the element. In late stages the three main 
branches give off numerous smaller ones, but these have been 
omitted in fig. 1 for the sake of clearness. 
Two or even three elements of this type are sometimes 
stained on the same side of a ganglion at one time. 
The element has stained in Th. III, Th. V—XI. In fig. 1, 
E Th. I1I, Th. V—VIII are inserted. 
an accident in putting it up. The drawing has, however, been made from this 
preparation, in preference to others, on account of the whole being more 
clear and satisfactory. 
