BILL AND HAIRS OF ORNITHORHYNCHUS PARADOXUS. 188 
it as formed from some cells of the old bulb which have not 
been used up in forming the old hair, and which have followed 
the shortening tube. 
I therefore believe that, accepting Gegenbaur’s account of the 
development of a hair, the most probable interpretation is still 
to regard it as morphologically equivalent to a scale or feather. 
When, however, we study this development in the very 
direction from which most help is to be expected, and ascertain 
the process which takes place in the most ancestral mammal, 
there can surely be no doubt about the matter. For the solid 
downgrowth of the higher mammals is replaced by an open 
tube in Ornithorhynchus. To an evolutionist this fact cannot 
fail to be the clear demonstration that the solid cylinder is the 
abbreviated representative of the open tube. With this fact, 
the significance of Gegenbaur’s distinction between feather and 
hair falls to the ground. - 
It is, indeed, by no means improbable that the first and 
earliest trace of the hair is formed at the surface in Ornitho- 
rhynchus, and subsequently sinks with the deepening tube. 
Material by which this suggestion could be tested is unfortu- 
nately wanting. 
But the open tube is not the only, although it is the most, 
important point about the development of the hair of Ornitho- 
rhynchus. The great length of the papilla projecting through 
‘the bulb into the lower part of the hair is also very significant, 
suggesting a previous development like that of a scale or feather 
from the surface of the epidermic covering of a papillary core 
traversing the structure from base to apex. 
Further confirmation is afforded by the axial rod of soft pro- 
toplasmic cells forming the medulla of hair; for a shortening 
papillary core, surrounded by cells of the rete mucosum super- 
ficially undergoing cornification, would tend to leave just such 
an indication of its former presence. 
This interpretation is strongly confirmed by the beautiful 
and detailed figures of A. Mertsching (‘ Beitrage zur Histologie 
des Haares und Haarbalges,’ ‘ Archiv fur mikrosk. Anatomie,’ 
1888, p. 32). Thus in pl. iv, fig. 1, he shows in human hair, 
