BILL AND HAIRS OF ORNITHORHYNCHUS PARADOXUS. 191 
EXPLANATION OF PLATES 14, 15, & 15a, 
Illustrating Professor E. B. Poulton’s paper on ‘‘ The Struc- 
ture of the Bill and Hairs of Ornithorhynchus para- 
doxus, with a Discussion of the Homologies and Origin 
of Mammalian Hair.” 
PLATE 14. 
The figures in this Plate illustrate the structure of the bill. The structure 
of the epidermis is indicated in Figs. 1 and 8. Figs. 1—7 deal with the 
tactile organs of the bill, Figs. 8—16 with the glands and their associated 
structures. 
Figs. 4, 8, 9, 10, 11, and 12 were drawn from sections stained with car- 
mine; while Figs. 3, 5, 6, 7, 18, 14, 15, and 16 were from sections stained 
with logwood. Fig. 1 was from a section stained with logwood and picric 
acid, Fig. 2 from one stained with carmine and picric acid. Cornified epi- 
dermic cells are indicated by a yellow colour. 
Fie. 1.— x nearly 200 diameters. Vertical section through the surface of 
the bill (probably near the edge of the superior surface of the upper bill), 
showing a complete push-rod and parts of two others. The convex upper 
end of each rod, surrounded by a slight ridge, is clearly seen. Each rod is 
seen to consist, for the upper fourth of its length, of extremely thin curved 
epidermal plates, retaining traces of nuclei surrounded by pigment (compare 
Fig. 2). The corneous layer is not nearly so thick in the push-rod as in the 
general epidermis of the bill. Below the upper fourth of their length the 
rods are formed of imbricated cells with distinct nuclei, the layers being better 
shown in more highly magnified figures (Figs. 3 and 4). The same applies 
to the axial group of longitudinal filaments and the circle of similar struc- 
tures shown in longitudinal section on each side of the group, and separated 
from it by a row of imbricated cells. The filaments are seen to diverge 
slightly at the lower end of the rod. Pigment is chiefly present at the 
sides of the rods, and especially among the lowest cell-layers forming the 
extreme base; but it also exists in the inner layers, as is shown in Fig. 4. 
The lower part of the rod is free from the general epidermis of the bill, 
being separated from it by a tubular dermal upgrowth, the upper part of 
which sends up papillary processes. Hence the dermis seen on each side of 
VOL, 36, PART 2,.—NEW SER. 0) 
