BILL AND HAIRS OF ORNITHORHYNOCHUS PARADOXUS. 1938 
not the radial form indicated in the diagrammatic transverse section. They 
are, furthermore, far less numerous than in the latter, each plate curving 
round the rod for a considerable distance, as is indicated by the arrangement 
of the nuclei in Fig. 3. 
Fie. 5.— xX about 50 diameters. Horizontal section of one of the highly 
sensitive transverse ridges on the outer side of the upper surface of the lower 
bill (inside the mouth). The push-rods seen in transverse section are ex- 
tremely numerous. Nearly all the layers shown in Figs. 3 and 4 can be made 
out, even with this low power. Fifteen gland-ducts are seen in transverse 
section, scattered between the twenty push-rods. In other parts these pro- 
portions are generally reversed. Many of the gland-ducts are surrounded by 
pigment. The right-hand upper push-rod has a distinct papillary upgrowth 
on each side of it. “Higher powers show that two or more such papillz are 
usually arranged round the other rods. 
Fic. 6.— x about 50 diameters. A deeper horizontal section, nearer the 
middle of the length of the same ridge as that which supplied the material 
for Fig. 5. The section passes just below the lower ends of the push-rods, 
and shows the numerous groups of Pacinian bodies (from two to five ina 
group), each of which is placed under a rod (compare Fig. 1). Twenty-four 
groups are represented, together with nineteen gland-ducts, the proportion 
being about the same as in the last figure. When only a single Pacinian body 
is seen, it is probable that the rest of the group was not included in the section. 
Many of the gland-ducts are surrounded by pigment. Between the struc- 
tures described is the dermis of the bill, which is concentrated to form a 
fibrous investment to both ducts and groups of nerve end-organs. 
Fic. 7.— xX rather over 400 diameters. A single group of Pacinian bodies 
from one of the ridges of the lower bill. The figure shows the essential 
similarity of these nerve end-organs to those previously described in the 
tongue of the same animal (‘ Quart. Journ. Micr. Sci.,’ July, 1883). 
Fic. 8.— X nearly 200 diameters. Vertical section through the surface of 
the upper bill, probably from the same locality as that described in Fig, 1, 
including a longitudinal section of a gland-duct on its way to the surface, 
together with the remarkable structures associated with it. The duct passes 
along the axis of an epithelial cylinder, which has many points of resemblance 
to a hair, shortened at both ends, so that it is flush with the general epidermic 
surface above, while its bulb is but little below the lowest layer of the epi- 
dermis. In favorable examples, however, as in that selected for figuring, 
the upper corneous end of the cylinder projects a little, and is surrounded by 
a distinct trench. Below the corneous stratum of the general epidermis the 
cylinder is surrounded by an epithelial layer (0. 7. s.), which presents many 
points of resemblance to an outer root-sheath, from which the cylinder is 
seen to be in part free, a distinct space between the two being visible on both 
sides a little below the level A and on one side at the deeper level C. Below, 
