THE GIANT EARTH-WORM OF GIPPSLAND. 19 
much less frequent, and as the nerves curve upwards, so as to enter nearer the 
dorsal than the ventral side, the few which are present are almost confined to the 
under surface. In Microcheta rappi,* Brennan figures the ganglion cells as present 
in greater numbers in the region of the lateral nerves, exactly the reverse of that 
which obtains in Megascolides. (3) An upper region where “giant fibres” are present. 
Each of these fibres is enclosed in a distinct encasement of connective tissue, 
continuous (see Fig. 19, gf) with the external and internal layers of this already 
described. The numbers of the “giant fibres” seen in section, varies in different 
parts of the cord. Right in the very front of the body, in the region of the sub- 
pharyngeal ganglion, only one, the central upper one of the figure is present (cf. Fig. 
10, gf-), a little further back two lateral ones are present in addition, and in very 
many sections, though not in all, a fourth median one is present, as in the figure. The 
great length of the worm precludes the cutting of continuous sections, so as to trace 
the exact relationship of the fibres, but they were traced, as in the figure, completely 
through one segment in the hinder region of the body. In another series of sections 
from the same region, the lower one of the four gave branches off to the two lateral 
ones and disappeared, the connective tissue septum then passing right up the 
median line through the space occupied in the figure by the “ giant fibre.” The three 
upper ones appear to be the main ones, and of these, the first seen in a series of 
sections passing backwards from the cerebral ganglia is the central one. (ef. Fig. 10, 
in which in the region of the pharynx, just posterior to the sub-pharyngeal ganglion, 
only the central fibre is seen). It commences in the very anterior region of the 
ventral cord, where it simply thins out and merges into the external connective tissue 
sheaths of the cord. The two lateral ones appear in a similar manner a little further 
down the cord, but no giant fibres appear, as in other earth-worms, to either (1) pass 
up the pharyngeal commissures, or (2) to have any connection with the nervous 
tissues. 
As to the structure of the fibres, they are describedt as being composed, of a 
“‘doubly-contoured sheath, with clear contents,” and as being “separated from the 
nerve cord by the inner neurilemma,” and “ embedded in a connective tissue-sheath, 
containing reticulate cells.” 
Benuam{ figures them with the double contour, and surrounded by a certain 
amount of connective tissue. In Megascolides (Fig. 19) each one is enclosed, as said 
above, in a very definite compartment of tissue (ct.), and each fibre itself has the 
nature of a rod, formed of a perfectly homogeneous material, which stains moderately 
with borax-carmine, and has, owing doubtless to the action of reagents, a 
somewhat irregular outline in section. At times a nucleus may, as in the figure, be 
* Op. cit. Fig, 37. 
+ “Forms of Animal Life,” Rotneston and Jackson, 2nd Edit., p. 212. 
t Op. cit., Fig. 38, 
