Introduction

Four names dominated the literature on eggshell composition and structure in the era when studies of the former were based on ‘wet’ chemical methods and those of the latter on light microscopy: von Nathusius, Romanoff, Schmidt and Tyler. Access to these early studies is easy. The pioneering studies of von Nathusius (1821-1899), who trained as a chemist, managed the family estate and studied eggshells as a hobby, were translated into English and published in a single volume by Tyler (1964). Romanoff collaborated with his wife, Anastasia, in the publication (1949) of the classic monograph, The Avian Egg. In 1969 Tyler reviewed the literature on many aspects of eggshell structure and composition and highlighted Schmidt's contribution to early studies of the crystallography of the mineral part of the shell. These four workers laid down a substantial staddle upon which later workers, blessed as they were with developments in electron optics, built up knowledge of eggshell structure and composition. There has been a tendency for such studies to be done in isolation. Little if any attempt has been made, however, to consider structure in the broad context of the breeding biology of birds.

Such isolation is no doubt due in part to the apparent independence of the avian embryo for much in the way of communication with the nest-bulk environment. Needham (1950) stresses the extent to which the avian embryo is closed off from the environment, the term ‘cleidoic’ (closed box) is used to designate this state.