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This work deals with the oxygen consumption of ostrich chicks during incubation. Brood eggs were incubated in a hermetic isolated acrylic-glass cylinder. Reduction of oxygen content in the air surrounding the egg was measured using an oxygen-sensitive electrode. A sigmoid curve could be drawn during incubation, with the steepest phase being around day 26. Maximum oxygen consumption was reached on day 36. It was slightly decreased until day 39, when the embryo switches to lung circulation, followed again by an increase until hatching. Average oxygen consumptions for the whole brood interval were calculated to 63.6 liters. Oxygen volumes consumed on day 36 result in a demand about to 240 liters of fresh air per egg and day. Oxygen consumption of the embryos on day 36 was significantly positive correlated with their vitality. Numb or less vital embryos could be clearly differentiated from others. The higher a chick's oxygen consumption, the earlier and shorter its hatching. Possible applications of the method in regard to the evaluation of incubation parameters or chicken constitution are discussed.

To contribute to the knowledge of the cranium of older bird embryos, the chondrocranium and osteocranium of the Black-headed Gull (Larus ridibundus) are described. The chondrocranium of the Black-headed Gull is compared with the chondrocranium of other bird species with special consideration of functional and phylogenetic aspects. As a result a "grundplan" of the bird chondrocranium is reconstructed. Most of the chondrocranial autapomorphies of birds are connected with the enlargement of the eyes, the development of a beak and a prokinetic skull, and the reduction of the olfactory system.

Chimeras produced from amphibian, mammalian, and especially avian embryos have provided important insights into vertebrate development. Important contributions have led to new concepts in understanding the development of, for example, the nervous system, the vascular system, and the skeletal muscles. The migration of cells is particularly accessible in chimeras. More important results are to be expected from chimeras in the future, especially by combining this approach with other state-of-the-art techniques.

Molecular genetics don't explain the behaviour of cells. It is well known, however, that changes in behaviour precede changes of genetic manifestation. Since only soma cells are working onto-genetically throughout life, they should be thought capable of evolutionary functions. Their precedence is possible because of their surplus of genetic outfit, and the soma cells even must precede from the zygote stage on when their "struggle for life" starts. This notion of Darwin ("struggle for life") should therefore be more emphasized as motor force than his other 2 notions: "variation" and "selection". The phylogenetic development of the egg-tooth of sauropsids is taken as an example for this change-over in evolutionary theorization.