The hatching sequence of ostrich (Struthio camelus) embryos with notes on development as observed by candling.

1. The hatching sequence of the ostrich (Struthio camelus) was determined by observing embryos during candling, those in the process of hatching and in dead-in-shell eggs. 2. Candling showed that there was a progressive increase in dark shadowing within the egg but fine details were not easily seen. Nevertheless candling is considered to be an important method of assessing development of ostrich eggs during incubation. 3. The ostrich embryo adopts a hatching position and follows a hatching sequence different from that of the fowl. During internal pipping, the air space is pulled towards the beak in the former but the beak moves to the air space in the latter. The right foot has an important role in breaking the shell during hatching. 4. The hatching process is considered to reflect an adaptation to the egg having a hard, brittle shell. 5. Malpositions in the ostrich may have been misinterpreted in the past because of the unusual hatching position. The commonest malposition described here was head-in-the-small-end.