BILL AND HAIRS OF ORNITHORHYNCHUS PARADOXUS. 185 
T entirely agree with Maurer that any explanation of the 
hair which fails to account for the inner root-sheath is a failure ; 
but I hope to show that a reasonable explanation is quite 
possible on the hypothesis that hairs and feathers are homo- 
logous. Indeed, when Maurer comes to criticise the parallel 
between a hair and a feather sunken in a follicle, I wonder that 
the homology between inner root-sheath and the appendicular 
parts of a feather did not suggest itself to him. Had he seen 
the strongly developed thick fibrous sheath of Ornithorhynchus, 
I venture to think that he might have come to a different con- 
clusion. 
The true significance of any peculiar structure in the higher 
members of a Class is to be best understood by the study of 
those lower forms in which its undoubted homologue is far 
more strongly developed. If we only knew of the hairs of the 
higher mammals, there would be a great deal to be said for 
Maurer’s theory. But it fails because it is framed to account 
for the Mammalian hair as it is, and not to account for it as the 
condition in Ornithorhynchus shows that it has been. Thus, 
his explanation of the inner root-sheath may fairly account for 
the structure as it is usually described, but it fails to account 
for it in the lowest mammal. Again, he explains hair as a 
radially symmetrical structure, but Ornithorhynchus shows that 
it is primitively bilateral. The same objection may be raised 
to his explanation of papilla and solid epidermic downgrowth; 
the explanations do not apply to Ornithorhynchus. 
As to his objection that mammals have nothing comparable 
to the moulting of scales in reptiles, it may be replied that the 
succession of hairs affords as close a parallel as the mechanical 
conditions of the case admit. Replace the flattened scale 
growing from its under surface by the solid slender cylindrical 
hair growing from its lower end alone, and it becomes clear 
that the flaking off of the corneous surface of the one can only 
be paralleled by the loss of the whole corneous cylinder of the 
other and its replacement by a fresh one. Furthermore, the 
new large hair is, in Ornithorhynchus, far advanced in develop- 
ment before the old one is shed. Hence there is exactly what 
