188 EDWARD B. POULTON. 
round its periphery. Giovauni’s account is important in this 
relation, proving that the inner root-sheath is at first formed 
over the apex of the future hair, and only assumes its normal 
relationship when the hair has grown through it. 
We have in woodcut fig. 2 the representation not only of 
the expanded tips of the larger hairs of Ornithorhynchus as 
they would be if they grew at the surface, but of flattened 
Ihe, Ye 
¢ py) , 
= ZA { Epidermis 
——— ——— ——t 
imbricated protective scales with a rich fibrous growth round 
their bases and sides, a growth which in the form of a thick 
continuous felted under-coat would be of the greatest assistance 
in maintaining a constant temperature. 
By far the most bird-like structures in Archeopteryx, as we 
know it, are its feathers. While its skeleton is profoundly 
modified from that of the typical bird, its feathers remain 
entirely typical. 
Among the most Mammalian structures in Ornithorhynchus 
are its hairs, and although they differ in some important 
respects from those of other mammals, their divergence is 
small compared with that of development, ovary, skeleton, &c. 
This extraordinary persistence of the epidermic characters of 
the Class when other Class characters are failing, suggests most 
strongly a persistence altogether beyond the limits of the Class, 
