BILL AND HAIRS OF ORNITHORHYNCHUS PARADOXUS. 199 
from within as well as in longitudinal section, and is clearly shown to consist 
of a network of corneous fibres enclosing longitudinal fusiform spaces through 
which the outer root-sheath (0. 7. s.) is seen. At the upper end the section 
becomes more tangential, and hence the more obliquely cut edge of the outer 
root-sheath gives an erroneous impression of greater thickness at this point. 
Fie. 25.— x nearly 200 diameters. A gland tube and duct opening into the 
bay between the flange-like posterior extension of the upper bill and the hairy 
surface of the head. The secretory part of the gland is seen to possess the 
structure typical of the Mammalian sweat-gland. The duct is, however, 
unusually wide. In this position the glands were peculiar in opening on the 
surface independently of hairs or hair-like epidermic processes. 
PLATE 15a. 
The young Ornithorhynchus paradoxus of which the hairs are de- 
scribed in this paper, and are represented in Plate 15, figs. 19—24. The 
animal is represented of the natural size, as seen from the left side in Fig. 1, 
from the ventral aspect in Fig. 2. The skin appeared to be quite smooth and 
bare, but closer examination showed that the tips of the large hairs had 
emerged from the surface, the small ones being still concealed beneath it. 
