Summary. Two tvpes of .spleen eoloii}' fi)niiation ha\e been f()iiipart.'d with respect to the kinetiLs nf er\thn>id cells. KndoHenoiis colonies were obtained using phenjihydrazhie treatment followed by lethal total body irradiation und exogenous colonies derived from normal bone marrow transplanted into irradiated animals. Individual colonies of both endogenous and exogenous types were scored for ''HTdR labelling index (LI), mitolic index (MI) and \ineristine niitotic accunuilatioii. There was no significant dilierence in kinetic beha\'iour of erythroid colonies in the endogenons compared with the e.\ogenoiis situation.Erythroid colonies from both endogenous and exogenous sonrees were classified into three separate groups, "early", "intermediate" and "late" on the basis of their inori) ho logical appearanee. When this classification was later taken into account there were no differences in kinetic behaviour between "early", "intermediate" and "late" colonies of endogenous as comparctl to the respective classes of exogenous colonies. Labelling indices of "early", "intermediate" and "late" colonies fell into three distinct groups ha\ing mean corrected labelling indices of approximately 15%. b3% and 47'/, rcspecti\el\. The mean nuclear diameter of cells in "early" colonies was significantK-greater than of cells in "intermediate" and "late" colonies, cells of the latter two having similar mean nuclear diameters.The only significant difference observed between the endogenous and exogenous colonies was that the erythroid to granulocytic colony ratio was considerably higher for endogenous colonies. This ma\-be attributed to the presence of an environment more fa\ourable to er>throid ile\elopinent in spleens of miee which ha\e haemoKtic anaemia.INTRODUCTION.

Summary Both Unit Gravity Sedimentation and Counterflow Centrifugation separate cells primarily on the basis of size, However, when performed concurrently on the same normal mouse bone marrow cell suspensions, Unit Gravity Sedimentation was found to be far superior in terms of the recovery of total nucleated tell loud and the recovery and enrichment of two classes of functional progenitors: (1)those responsive to the combined stimulus of pregnant mouse uterus extract (PMUE) plus human spleen conditioned medium (HUSPCM), and (2), those responsive to PMUE alone. Neither technique was able to resolve PMUE from PMUE + HUSPCM progenitors. The major limitation of Counterflow Centrifugatton for the separation of sub‐populations of marrow cells is related to the complexity and range of cell sizes in marrow cell suspensions which lead to significant pellet formation within the elutriator chamber. Furthermore, cells undergoing Counterflow Centrifugation are subjected to forces not encountered in Unit Gravity Sedimentation. Therefore, the basis of the separations is not identical and this is reflected in cell volume distributions of comparable fractions separated by each method.

Social interactions are fundamental properties of gregarious species, helping to establish dominance hierarchies and maintain social bonds within groups, thus having significant effects on fitness. Cattle (Bos taurus) are social ungulates which engage in affiliative and agonistic relationships with other individuals. Although there are approximately 1.5 billion cattle on the planet, the opportunity to research cattle behaviour in free-ranging groups is rare, as there are few feral populations worldwide. Cattle engage in positive social behaviours such as allogrooming, where one individual licks the body of another. The relationship between affiliative behaviours and other individual characteristics (such as sex and dominance status) are frequently studied in other gregarious species, but are largely undetermined in cattle. To investigate the relationships between sex, dominance status and allogrooming, we observed a mixed-sex feral cattle herd in Hong Kong, recording dominance interactions and allogrooming events. We found that dominant females received more allogrooming than subordinate females, but subordinate females did not perform more than dominant ones. Males performed allogrooming more towards females than other males, but females groomed both sexes equally. Sex affected dominance position, with males obtaining higher status than females, but not all females were subordinate to males. These preferential allogrooming patterns improve our knowledge of sex-specific interactions, and help us to understand the dynamics of agonistic and affiliative behaviours in multi-male, multi-female ungulate groups. Studying a free-ranging feral population provides us with a unique insight into ungulate behavioural patterns and the evolution of cattle social behaviours.