The development of the haematopoietic tissues of the tammar wallaby Macropus eugenii follows a similar pattern to that observed in eutherian and other metatherian mammals. At birth, the liver appears to be the only site of haematopoiesis with significant numbers of neutrophils and stem cells present in the circulation. By Day 3, the spleen shows limited haematopoietic activity and by Day 12 contains areas of erythroid and myeloid cells. At two weeks after birth, the haematopoetic activity in the liver declines and small areas of haematopoiesis are apparent in the bone marrow. By the end of the first month, the bone marrow appears to be the major site of haematopoiesis.

Immunoglobulin G (IgG) was measured in fetal, neonatal and colostral samples from the tammar wallaby (Macropus eugenii) in order to study the possibility of passively acquired immunity. Samples were obtained from young at a known stage of gestation and at known times (to the minute) after birth. IgG was present (in increasing levels of concentration) in fetal serum, neonatal serum and colostrum. Since the fetus and neonate are probably unable to make immunoglobulin (Ig), it is hypothesized that transplacental and trans-gut transmission takes place from mother to offspring. The vascular yolk sac placenta has a high concentration of IgG, and is the most likely route of transmission from mother to young. Some observations were made of IgA which was found only in colostrum. No Ig of either kind was found in yolk sac fluid.

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