Follicle Development in the Australian Merino

Abstract

So far as we are aware, there is no published information of a quantitative nature on the post-natal development of the follicle population in the skin of the merino sheep, although Carter and Hardy¹ have presented quantitative data for the pre-natal period. In his classical description of the development of the follicle group, Carter² was concerned with descriptive morphology and ontogenic considerations rather than with quantitative aspects. His clear definition of the two follicle types (primary and secondary), their relative place in the developmental sequence, and their fundamental arrangement in group form lays the foundation on which quantitative considerations may be built. The most satisfactory measure of the progress of development of the follicle population is the ratio of secondary follicles to primary follicles (S/P). The validity of this unit rests on the observation (Carter²) that the primary population within any region is determined by approximately the eighty-sixth day of pre-natal life, and that only secondary follicles develop thereafter. While it has not been proved that no primary follicles develop after this time, the histological evidence is heavily in this direction.