47 
epithelium, although not themselves passing to the surface, 
detach from their outer extremities, by repeated division of 
their nuclei and cell-walls, a series of progeny one after 
another, from which are derived the other strata. The proof 
that this is not the mode of growth of the corneal epithelium 
of the ox is that the columnar cells have never more than 
I one nucleus each, and none of them present any trace of such 
budding ; and also that the superjacent digitated cells are 
larger than those more superficial. Altogether there can be 
little or no doubt that the cells of the columnar stratum are 
derived from corpuscles which grow inwards, and that the 
spindle-shaped cells above described are, some of them, 
' destined to become developed into columnar cells. We 
i must suppose that the digitated cells are developed in the 
! same manner ; and in that case the corneal epithelium may 
be regarded as having its germinal stratum in its middle 
depth, from which growth proceeds towards both the cornea 
and the free surface. 
The degenerated cells with air cavities, found in the 
deepest stratum, point to a circumstance not hitherto ob- 
served, nor possibly suspected, namely, that the old elements 
of a stratified epithelium are not always thrown off at the 
surface ; for in this instance they degenerate and disappear 
in their original position, their parts being doubtless ulti- 
mately absorbed, in like manner as a degenerated muscular 
fibre is absorbed in the uterus after labour, or in a striped 
muscle. 
While, however, the importance of the preceding observa- 
tion consists principally in demonstrating the possibility of 
modes of growth more or less similar to that described in the 
corneal epithelium of the ox occurring in other stratified 
epithelia, it is not hastily to be presumed that the growth of 
the general epidermis necessarily proceeds in the same way 
as that of the corneal epithelium. In particular, it must be 
recollected that the corneal epithelium is uniquely situated in 
being spread over a non-vascular texture, and in being con- 
tinuous at its periphery with a denser epithelium which has 
blood-vessels beneath it ; and it may be therefore fairly ques- 
tioned how far it derives its nourishment from beneath, and 
how far from the vessels around it. 
A further investigation into the growth of the cuticle is 
naturally suggested by the facts now brought forward, and I 
have to regret that as yet I have not had time to pursue that 
subject with sufficient care. But I may' mention that in the 
deep parts of a delicate piece of cuticle I have been able to 
see cells with the nucleus partially replaced by a cavity, and 
others in which it was wholly so. 
