36 EDGAR J. ALLEN. 
The element F (0) (fig. 1), which occurs in Th. x and x1, 
resembles the element F (Pt. I, pl. 35, fig. 1), and may be the 
representative of that element in these two ganglia. 
The element P, Th. vi (fig. 1), presents a striking appearance 
when stained, and differs in important respects from the 
elements previously described. ‘The cell lies in the anterior 
portion of the lateral mass of ganglion-cells. The fibre curves 
backwards to the neuropile, and after giving off what, from its 
relatively small diameter, may be regarded as a subsidiary 
branch, divides into two main branches, one of which passes 
immediately out of the ganglion through the anterior nerve- 
root, whilst the other runs across as a stout transverse fibre to 
the opposite side, where it turns back again forming a loop 
with itself, and was traced as far as the centre of the ganglion. 
When the element has stained upon both sides the two trans- 
verse branches lie close together and appear as one stout fibre. 
The subsidiary branch, which leaves the fibre before it bifur- 
cates, takes the somewhat complicated curved course repre- 
sented in the figure, and was traced to the neuropile of the 
opposite side. As, however, neither this nor the main branch 
was observed to break up into finer branches, it seems pro- 
bable that the staining was in all cases somewhat incomplete. 
Similar elements have not been found in any other ganglion. 
ProspaBLeE Motor ELemeEnts or Posterior Roots.—The 
cells of the elements just described all send out fibres through 
the anterior nerve-root of the ganglion in which the cell is 
situated. In the two following cases, however, the fibre leaves 
by the posterior root. 
In Th. vist, an element (fig. 1, K, Th. vir) similar to K, 
Th. 111 (Pt. I, pl. 35, fig. 1), has stained. The cell is situated 
in the central mass of ganglion cells, the fibre decussates with 
its fellow of the opposite side and passes out at the posterior 
root of the ganglion. This element has been found only in 
Then and Th. vars. 
In Th. x1 is an element which most nearly resembles the 
element J of the anterior ganglia. This is denominated J (3) 
(fig. 1). The cell is situated at the posterior end of the central 
