144 EDWARD B. POULTON. 
I. IntTRoDUCTION. 
In the summer of 1884 I made a communication “On the 
Tactile Terminal Organs and other Structures in the Bill of 
Ornithorhynchus” to the meeting of the Physiological Society 
at Oxford. A short account, containing however the chief 
results, was published in the Proceedings of the Society (‘ The 
Journal of Physiology,’ 1884, pp. 15, 16). In searching for 
the terminations of the abundant medullated nerves I found 
two remarkable structures in the epidermis of the bill :— 
(1) Epithelial rods which appear to convey the effect of surface 
pressure to a group of nerve end organs resembling Pacinian 
bodies. These rods, from their obvious analogy to the push 
of an electric or, better still, pneumatic bell, may be con- 
veniently called “ push-rods.”’ (2) Other epithelial rods 
along the axis of which passes the duct of a gland. These 
rods resemble in certain respects a shortened and truncated 
hair. 
The interpretation of these latter rods as modified hairs was 
disputed at the meeting by Dr. Klein, but supported by Pro- 
fessor Schafer. This controversy and the obvious interest of 
the inquiry led me to undertake further work, which included 
an investigation of the hairs covering the body of this animal. 
From time to time this work has been continued from 1884 up 
to the present date (December, 1893), and many drawings 
have been made and discussed with friends, although until now 
T have published nothing more upon the subject. During the 
summer of last year (1892) I worked for some weeks in the 
laboratory of my friend Professor Lankester, at which time the 
drawings were arranged and the description of Pl. 14 written. 
Within the last few days the recent description of the push- 
rods by Professor J.T. Wilson and Mr. C. J. Martin (‘ Macleay 
Memorial Volume,’ pp. 190—200) has reached me. I was 
prepared to find that their investigation would have rendered 
any further publication on this point unnecessary, inasmuch as 
fresh material had been available, the want of which had 
confronted me throughout, and especially in the attempt to 
