Witson anp Martin —Rod-ke Tactile Organs tn the Muzzle of Ornithorhynchus. 197 
the lines af in fig. 15. In some transverse sections of the rod they appear to nearly 
fill the centre of the core (fig. 13, Pl. xxv.), while in others they are arranged as a 
circle around the centre (fig. 6, Pl. xxiv.). 
Oo 
The peripheral series of nerve-fibrils form a complete circle running vertically 
from near the base to the surface, and situated between the epithelial conical laminze 
which constitute what we have designated the core (c, in fig. 15), and the layer of 
imbricated cells outside this (vz, fig. 15). They are shown as a circle of dots in this 
position in the transverse sections (fig. 6, Pl. xxiv., and fig. 13, Plate xxv.). 
The medullated nerves from which these fibrils spring enter the sides of the 
organ a short distance above the base (figs. 19 and 21, PI. XXVI.). 
After entering they speedily lose their medullated sheaths and give rise to a 
number of small fibrils, which find their way amongst the epithelial cells forming the 
basal portion of the organ [and so far not arranged into any definite circular series, 
21 
Pl. xxvz.)|, until they arrive between the core and the layer of imbricated cells. 
such as was described above in the more superficial part of the organ (fi 
8: 
They then run vertically upwards in a parallel course to the surface. 
The fibrils of both groups present a very characteristic appearance ; they are 
finely and closely varicose throughout, and the varicosities are situated all at the 
same levels in each of the parallel fibres of the groups. These varicosities occur in the 
intervals between the superimposed epithelial elements, as is semi-diagrammatically 
shown in fig. 15, Pl. xxvi. They can be seen both in the stained and unstained 
specimen. In fig. 12, Pl. xxv., and fig. 22, Pl. xxvr, there is represented a specimen 
stained with hematoxylin, by which the fibrils are left unstained, showing a broken 
rod-like organ, from the fractured end of which the varicose fibrils may be seen 
projecting, like the antennz of some insect. The fibrils, however, are best seen in 
fig. 21, Pl. xxvi., which is a drawing from a section stained by gold chloride by 
Freud’s method, by which these structures are very beautifully brought out as deep 
purple or violet limes, whereas the surrounding structures are only faintly stained. 
The nerve fibrils can be traced almost, if not quite, up to the convex free surface 
of the rod; but towards the surface they are only faintly discernible, as they, along 
with the epithelial elements of the rod, participate in the corneous change which the 
superficial layers of the epidermis undergo. This corneous change, however, is never 
so complete as to obliterate the contours of the cell elements and nuclei either in the 
structure of the rods or in the surrounding epidermis. 
In conclusion, we have pleasure in expressing our best thanks to Dr. T. H. 
Barker, of Wellington, N.S.W., for his kindness in procuring and forwarding the live 
