158 EDWARD B. POULTON. 
4 Van dE Haven.—‘ Mémoire sur le genre Ornithorhynque,” ‘Nova 
Acta’ (Bonn), 1823. 
5. Péron and Lesurur.—‘ Voyage de découvertes aux Terres australes 
pendant les années 1800—1804.’ 
6. Mrecxet.—‘ Ornithorhynchi paradoxi descriptio anatomica,’ 1826. 
7. Lryp1e.—‘“‘ Ueber die ausseren Bedeckungen der Saugethiere,” ‘ Arch. f. 
Mikr. Anat.,’ 1859. 
8. WetcKer.— Ueber die Entwickelung und der Bau der Haut und der 
Haare bei Bradypus,’’ ‘ Abhand. Naturf. Gesell. zu Halle,’ ix, 1866. 
9. Wa.pEYER.—‘ Atlas den Menschlichen und Tierischen Haare,’ 1884. 
10. Souza Fontes.—‘ Beit. z. Anat. Kenntniss der Hautdecke des Orni- 
thorhynchus,’ Dissert. Inaug., Bonn, 1879. 
11. MeErEe.—‘Over de Haren der Zoogdiere,’ Inaug. Dissert., Amsterdam, 
1893. 
2. General Structure and Arrangement of the Hair. 
The hair-like appearance of the epidermic cylinders in the 
bill led me to investigate the hairs of the body generally, and 
although the results seem to have no special bearing on the 
significance of the former structures they are of much value 
and interest on their own account. 
This research was undertaken in the winter of 1887-8, 
when all the figures (except fig. 24) represented on P1]. 15 were 
drawn. Since then it has been renewed from time to time, 
special attention having been devoted to the subject in Pro- 
fessor Lankester’s laboratory dnring the summer of 1892. 
Over the general surface of the body and head of Ornitho- 
rhynchus we meet with large hairs, each of which is attended 
by bundles of small hairs. Furthermore, on the dorsal area at 
least, each large hair is attended by a constant number of four 
bundles of small ones. The latter commonly vary in number 
in the dorsal region from seven to twelve in a bundle, and all 
emerge in a sheaf from a common follicular mouth. The 
four bundles are arranged on each side of and behind the 
larger hair, and, as all slope obliquely backwards, the shafts 
of the small hairs lie beneath that of the large one belonging 
to the same group. 
The protective large hairs are evidently subject to much 
wear and tear, and succeed each other very rapidly; the new 
