In connection with a sheep hybridising experiment which is being carried cut by the Animal Breeding
Research Department, a microscopical analysis of the
fleece of the parental breeds involved (viz. Scuthdown
and Blackface Mountain) was undertaken. It was hoped
in this way to make a complete survey of all British
breeds, describing in the first place those which are
most frequently used for crossing on account of their
greater value in the study of the inheritance of
fleece characters. However, this study had not long
been commenced, when it became evident that if the
original method of examining each breed separately and
thoroughly in sequence were adhered to, while useful
data would be collected in large numbers, much of the
significance of such infcrmat ion would only be exposed at the end of the investigation, or indeed some
points would be entirely lost sigh of if they were
not accentuated until some breed towards the middle of
the series was reached. Moreover, the time required
to carry cut the work on such a scale would stretch
over many years.Accordingly, the position was reconsidered and
it was decided that the quickest way to optimum
results lay in first carrying out a breed survey on
the smallest scale compatible with reasonable accuracy
in general and basic results. Such a study would at
least present a bird's eye view of the situation and
would, in all probability, show or suggest more specific lines of research which might be followed with advantage.The work was carried out at the Animal Breeding
Research Department, the University, Edinburgh, and my
best thanks are due to Dr F. A. E. Crew, Director, for
the facilities and opportunities afforded to me during
the course of this investigation. I am very deeply
indebted to Professor Barker, University of Leeds, for
his kindness in supplying me with most of the wool
necessary for this study.1. Two main types of fibres occur in British breeds
of sheep. Type I is proportionally the longer
and coarser and exhibits c iaracteristic scale
markings. It appears to occur only in the
Lustre and the Mountain Longwool groups of
breeds. Type II ir shorter and finer and possesses a coronal type of scale marking; it occurs in all breed groups. It constitutes the
main type in the Short Wools, is present in
varying proportion in the Mountain Longwools
and the Lustres. In some samples of the latter
group, however, its component fibres are very
few in number.2. Two small subsidiary classes of fibres are also
found. Kemp, the coarsest type, is present in
all breeds. It is shorter than the main types
and is shed periodically, being usually found
l ir.g loosely in the fleece with a complete
tip &nc root. The other small group consists
of very fine short fibres similar in structure
to the finest members of type II. They were
only identified in a few of the samples, but
it is possible that they were present in all
breeds but were not separable from type II.3. Type I and kemp are considered to be homologous
with the hair of the primitive breeds of
sheep, while the primitive wool is represented
in modern breeds-by type II and the small group
of fine fibres.4. Medulla. varies greatly even within individual
breeds. It has a greater tendency to appear
in the homologues of primitive hair than those
of wool, and occurs more frequently in the
Mountain than in the Non-mountain wools. It is
suggested that this variability is not wholly
due to hereditary influences but is in some
measure caused by environment
