384 Proceedings of Boyal Society of Edinburgh. [sess. 
stalk, until near the root it is almost completely absent. It is 
apparently disintegrated in various places in the hair shaft. The 
most obvious character of these hairs is their remarkably short and 
stout form, being, relative to their length, much thicker than those 
of the other zebras, but actually very slightly thinner than those 
of the Burchell’s zebra, that is, taking the measurements in the 
thickest part of the hair in each case. Sections through the hairs 
of the mane, like those of the Burchell’s zebra, are circular almost 
throughout. The line of demarcation between the cortex and 
medulla is also almost regularly circular. The pigment is seen 
to be distributed pretty equally throughout the cortex, but has a 
slight tendency in places to be thicker nearest to the medulla and 
thinner towards the cuticle. This tendency was not apparent in 
the section from which fig. 6 was drawn. 
The extreme shortness of the hairs on the side of the body can 
hardly be ascribed to want of vigour caused by the environment 
in which this zebra lives, for, as Nathusius points out, the hairs of 
the Somali ass, which lives under the same climatic conditions, 
are longer and better developed than those of any of the other 
wild asses. 
Equus caballus. 
The hairs of the horse, as might naturally be , expected in a 
domesticated animal of which there are very numerous breeds, 
show extreme variability, so that it is practically impossible to 
state any characters which are applicable to all varieties of the 
species. The section figured, which is through a mane hair of 
Professor Ewart’s “ Circus Girl,” the foal of a skewbald Iceland 
pony by a Shetland pony, is fairly typical. The characters there 
seen, such as the fine granular appearance of the evenly distributed 
pigment, the clear and regular line of demarcation between cortex 
and medulla, and the relatively narrow cortical region, are very 
common in transverse sections of mane hairs of horses. The 
shoulder hairs, speaking broadly, show a weaker development of 
the medulla and a thicker cortex than in any zebra hairs. Of 
course the length, breadth, and fineness of horse hairs are especially 
variable and depend largely on the breed. 
Nathusius, who has but briefly described zebra hairs, has devoted 
