152 EDWARD B. POULTON. 
ending in a disc which separates “two clear vesicular cell-like 
structures.” This form of ending evidently needs the fresh 
tissues for its demonstration. 
At first sight the push-rods appear to be modified hairs, but 
the examination of their minute histological details does not 
support this comparison. It is possible, however, that they 
may be found to have some bearing upon the recent suggestion 
that the Mammalian hair corresponds to an epidermic tactile 
organ of the lower Vertebrata. However this may be, the re- 
semblance to the Mammalian hair as it now is, in my opinion, is 
far less close than that of the epidermic structures associated 
with the ducts of glands which open on the surface of the bill. 
Souza Fontes, in 1879 (‘ Beit. z. Anat. Kenntniss der Haut- 
decke des Ornithorhynchus,’ Inaug. Dissert., Bonn), men- 
tioned and figured these structures and the gland-ducts 
described below, but the paper is quite unworthy of mention. 
Indeed, the principal feeling evoked by a glance at the Plate is 
one of surprise at the system which can confer a University 
Degree for such a production. 
III. Tue Guanp-pucts or THE BILL AND STRUCTURES 
ASSOCIATED WITH THEM. 
The gland-tubes of the bill, and, indeed, of the general body 
surface, closely resemble the Mammalian sweat-glands, the 
secretory part of the tubule being wider than the duct, and 
lined with short columnar cells surrounded by a longitudinal 
layer of smooth muscle-cells (fig. 8, g/d.). The wall of the 
duct is composed of nucleated, probably polyhedral, cells, 
indistinctly marked off from one another in my sections. 
These cells are separated from the lumen by a cuticle, repre- 
sented as a row of thin, deeply staining, plate-like structures 
resembling nuclei (fig. 8, d’, transverse section; below d longi- 
tudinal section). Externally the tubes are surrounded by a 
membrana propria, in which nuclei are especially distinct in 
the transverse section of the duct (d’). 
The existence of such typical structures in the most primi- 
tive mammal indicates that sweat-glands are among the most 
