1900 - 1 .] Mr F. H. A. Marshall on Hair in the Equidce. 377 
tends to disappear towards the root. The manner of its disappear- 
ance is an open question. Mertsching,* after referring to certain 
statements by Kolliker that the frequent absence of the medulla 
in coloured human head hairs, and its almost regular occurrence in 
white head hairs, says that this points to the inference that the 
formation of the medulla is connected with the turning grey of 
the hair. This, however, cannot apply to equine hairs. But the 
colour of a hair to the naked eye is affected by the breaking down 
of the medulla, such hairs appearing considerably duller and 
darker. Thus light brown hairs become dull brown. 
Speaking generally, then, equine hairs may be said to be 
characterised by the invariable presence of the medulla to a 
greater or less degree of development, and by the tendency of the 
medulla to disappear at irregular intervals, leaving air spaces of all 
sizes. This latter characteristic appears in Waldeyer’s figure of 
horse hair, but not in his figures of the hairs of other Mammalia. 
Another character by which the equine hairs may be dis- 
tinguished from other hairs, and from hairs of other species in the 
genus, is the distribution and arrangement of pigment in the cor- 
tex. Nathusius f has called attention to the fact, which I have 
often observed, that in some species of the genus Equus , the pig- 
ment granules on one side of the medulla may present a different 
coloration to those on the other side ; in other words, that the 
hair may be striped longitudinally. This character, so far as I 
have observed, does not hold good for horse hairs, but it is very 
general in other members of the family. The hairs in such cases 
are coloured by at least two different sorts of pigment, which have 
blended unequally on the two sides of the hair. In this connec- 
tion, it is interesting to repeat for equine hairs some of Sorby’s J 
experiments on human hairs. When brown hairs of the type in 
which longitudinal striping is common are dissolved in a strong 
* Mertsching, “ Beitrage zur Histologie des Haares und Haarebalges,’’ 
Arch.f. MiJcr. Anat., Bd. xxxi. 1888. 
t Nathusius, “ Uber die taxionomische Bedeutung der Form und Farbung 
der Haare bei den Equiden,” Verhand. d. Deut . Zool. Gesellschaft auf der 
zweiten Jahresversammlung zu Berlin , June 1892, Leipzig, 1892. 
t Sorby, “ On the Colouring Matters in Human Hair,” Journal of Anthrop. 
Inst ., vol. viii. 
