BILL AND HAIRS OF ORNITHORHYNCHUS PARADOXUS. 195 
which surrounds the lower part of the epithelial cylinder traversed by the 
duct. The cells immediately round the duct tend to split away from those 
placed more peripherally, suggesting the separation of a hair from its outer 
root-sheath. 
Fic. 11.—Transverse section of the duct at about the level marked C in 
Fig. 8. This is the region of the bulb of the supposed hair. The difference 
between the epithelium of the duct (d.) and that of the supposed bulb is 
clearly shown, although the duct resembles that which is seen at a rather 
lower level than C in Fig. 8. The deeper staining of the duct (d.), and 
especially of its innermost layer, is very characteristic in these sections. The 
supposed cuticle (c.) and outer root-sheath (0. 7. s.) are clearly seen. 
Fic. 12.—Transverse section of the duct at about the level marked D in 
Fig. 8. The duct is surrounded by the ganglion containing many ganglion 
cells. One of these is seen to give off a long process; a medullated nerve- 
fibre with a node of Ranvier is also present. Both the duct and the ganglion 
are surrounded by a fibrous sheath. 
The following three figures represent various forms of the duct; all are 
magnified about 50 diameters. 
¥1G. 13.—The coiling of the duct in the lower end of the epithelial cylinder 
(the supposed hair) is well seen. The resemblance of the upper end of the 
cylinder to a truncated hair is especially distinct in this and Fig. 15. An S-like 
curve of cylinder and duct in the upper layers of the epidermis is shown in 
this and Fig. 15. It is a very common appearance. 
Fic. 14.—A very common form at the posterior part of the upper surface 
of the upper bill. 
Fic. 15.—A form in which the epithelial cylinder is very slightly developed. 
It occurs intermixed with those of the commoner type (Figs. 8 and 13). 
Fic. 16.— x nearly 200 diameters. This figure shows the form of two 
ducts, &c., in the bill of a young Ornithorhynchus, 8°3 centimetres long in 
the curled-up attitude. The ‘ bulbs” at the lower end of the cylinders are 
not only extremely well developed, but are more deeply placed than in the 
mature animal. Just below the level of the bulbs, large medullated nerves 
(diagrammatically rendered in the figure) extend in a horizonta layer, uniting 
to form ganglia round the bases of the bulbs themselves. It is very un- 
fortunate that histological details could not be made out. 
