BILL AND HAIRS OF ORNITHORHYNCHUS PARADOXUS. 169 
In the case of the small hairs, however, we do not meet with 
two in any of the single follicles; and here the old hair is 
shed before the tip of the new one reaches its base, or, as I 
think more probable, a new follicle is formed, perhaps from the 
point which represents that at which the earliest follicles were 
budded out from the first single tube. 
6. Recapitulation of Essential Peculiarities of Hair 
of Ornithorhynchus as compared with that of 
Higher Mammalia. 
In order to draw the conclusions which, as I believe, follow 
from the investigation of these structures in the lowest mammal, 
it will be convenient to recapitulate, making a short statement 
of the points in which the hairs differ from those of other 
Mammalia. 
In the GRouPs OF HAIRS we notice a marked bilateral sym- 
metry (fig. 17), and a definite relation to the bilateral sym- 
metry of the body itself. 
In the tance Harrs there is (1) a most distinct bilateral 
symmetry in shape, in structure (differentiation of upper and 
lower surface), and in succession, and a definite relationship 
to the bilateral symmetry of the body. The terminal shields 
are scale-like, especially in the tail, where they become 
sessile. 
(2) The inner root-sheath is of immense size (especially in 
the tail), and possesses a definite and peculiar structure, being 
formed of longitudinal corneous fibres united into a network. 
(3) The bulb and papilla are extremely large, the latter 
penetrating the base of the hair. 
(4) The hair is developed in a tube, which is open to the 
surface,—-in a tubular and not a solid downgrowth from the 
epidermis. 
The sMALL HAIRS are (1) arranged in bundles, which are bi- 
laterally disposed in relation to the large hair, and have a 
definite relationship to the bilateral symmetry of the body, 
although the shape and structure of the individual hairs is not 
