148 EDWARD B. POULTON. 
Muzzle of the Ornithorhynchus,” by Professors J. T. 
Wilson and C.J. Martin; ‘Macleay Memorial Volume,’ p. 180). 
In this country, where we see only dry or spirit-preserved 
specimens, it has generally been looked upon as a tough, horny 
structure. The glands to be described below are doubless 
responsible for the humidity, although they may also, as I 
have suggested (‘The Journal of Physiology,’ 1884, p. 16), 
secrete a substance which protects the skin from the prolonged 
action of water. 
Wilson and Martin describe structures in the horny teeth 
which they believe to represent push-rods which have under- 
gone cornification (Il. c., p. 192). 
In offering this interpretation I believe that they have mis- 
taken for push-rods the columns of cells which extend from the 
summits of the numerous papillz towards, and often as far as, 
the surface. These cells are much less cornified than those 
around, and stain readily; furthermore it may be said that 
the columns “ show a series of imbricated superposed cells,” 
although the arrangement differs in various details from that 
of the push-rods. The fact that a column invariably extends 
from the summit of a papilla, while a push-rod is invariably 
surrounded by two or more papillz, is sufficient proof that 
the two structures are not homologous. The structure of the 
cell-columns and their relation to the papille are clearly shown 
in my paper already quoted (‘ Quart. Journ. Mie. Sci.,’ July, 
1388, PL-TYV, figs. 4, 5,.8, 10,11); 
Speaking of the dermal sheath which surrounds the lower 
part of each push-rod, the above-quoted authors regard the 
rod as an epithelial downgrowth which causes “a depression 
in the summit of a dermal papilla” (1. ¢., p. 193). Inasmuch 
as two or more distinct papille arise from the upper edge of 
the dermal sheath (to be seen in section in PI. 14, fig. 3, accom- 
panying this paper ; and, by the eye of faith, in pl. xxiv, fig. 6, 
of the ‘ Macleay Memorial Volume ’), I should prefer to regard 
the rod as a modified interpapillary process, with the surround- 
ing papillz united into a continuous sheath below, while they 
remain free above. 
