658 
Proceedings of the Poyal Society 
As appendages of the skin they are liable, like all the epidermal 
growths, to great variation in structure, which is seen in its extreme 
form in the feathers of birds, and in the horns, hoofs, nails, and 
claws of the higher mammals. 
Apart however from these great variations, there are a number of 
smaller modifications, which, while they do not present the same 
structural interest, are of considerable value, as indicating differences 
in the breed of varieties of the same species, and are often of great 
industrial importance. 
Many of these smaller variations having come prominently under 
my notice, especially in the case of wool, in a series of researches 
extending over many years, in regard to the industrial classification 
and use of these fibres, I thought it might be of interest to the 
Fellows of the Royal Society, if I communicated a short record of 
the more important variations which I have noticed. 
Notwithstanding the many researches which have been made in 
this country, and especially in Germany, on the structure of animal 
fibres, they have hitherto been mainly directed to the variation 
existing between fibres and hairs in general rather than in particular ; 
that is to say, to the variation in structure occurring between the 
hairs and wools of different species of animals, rather than those 
differences which are found to obtain between hairs on animals of 
the same species and on the same individual. 
It is to these specific differences in the individual hairs and wool 
fibres of sheep and other allied animals that I wish to call your 
attention. 
The observations have for the most part been made on the fibres of 
wool which have a commercial value, and were undertaken originally 
for technical purposes, but they have also a special scientific signifi- 
cance, as indicating the constant tendency in nature to a reversion 
to a more primitive type, and in exhibiting that wide variation which 
is produced by environment and artificial selection in breeding. 
The difference in structure existing between wool and hair is one 
which is exceedingly difficult to define scientifically, and although 
in industrial practice amongst experts the distinction is well known, 
it depends upon such slight modifications that it is very difficult to 
determine where the characteristics of true hair cease, and those of 
wool commence, and vice versa. 
