The red kangaroo (Mcpalciti riifn, Di siniirest) luis an ocstnms c> cle of .15 days and a gestation period of 33 days. Following the birth of a younji. mating at post-partuiu oestrus results in the tlf\i'lopuicut of a lilastocyst. which reuiains ijuiescent in tlic uterus. About a month before the end of pouch life, or after the young is removed prematurely, tbe blastocyst resumes growth and a new pouch-young is born in 31 days. Within 2 days post-partum oestrus occurs, follcjwed by lactational anorstnis. The induction and maintenance of the (piiescent phase of emimonic development is associatfd with the tactile stimulus of the suckling young (Shannan. 1964), This process iif (Iel;iyc' and appearance of the milk from uung will be referred to as gland 2. After the birth of the second young, the first young no longer entered the poiich but continued to suckle mammary gland 1 from outskle the pouch.•Present addlress:

Two hundred and twenty six multiparous Friesian and 185 multiparous Jersey cows on nine dairy farms were inseminated with semen from four bulls (one Friesian, one Hereford and two Charolais) and conception and calving data were recorded. There were no significant differences between sires or breed of dam with respect to still-births, calving difficulties or conception rates. Both sire and sex of calf significantly affected gestation period, sex in the case of Friesian cows, and sire in the case of Jersey cows. Breed of dam and sex of calf significantly affected birth weight, calves out of Friesian cows being heavier than those out of Jerseys, and male calves heavier than females. Calves were transported to the Research Centre and artificially reared using milk replacer and weaned onto a barley based concentrate ration at 6 weeks old. Rearing mortality was high, particularly in those calves sired by Charolais bulls. The major cause of death in these calves was a self starvation-scouring syndrome of undetermined cause. At 12 weeks old, sire had no significant effect on liveweight of calves out of Friesian cows, but did affect calves of Jersey cows. For male calves, those sired by the Friesian bull and Charolais number two were significantly heavier than those by Charolais number one and the Hereford. For female calves a similar result was obtained except that Charolais number one was also not statistically different from the Friesian and Charolais number two.

SummaryElectrophoretic examination of the haemoglobins of a sheep-goat hybrid foetus indicated the presence of haemoglobins found in the foetuses of the parent species only. No interaction products were found.In vitro "hybridization" experiments indicate that the difference in electrophoretic mobility between sheep A, sheep B, goat A, goat F, and sheep F haemoglobins is due to a difference in the non-ex-portion of the haemoglobin molecules. The absence of electrophoretically detectable haemoglobin interaction products in the hybrid foetus is explained by the finding that the ex-polypeptides of the parent species are electrophoretically indistinguishable.