Vaterite Deposition During Eggshell Formation in the Cormorant, Gannet and Shag, and in ‘Shell-less’ Eggs of the Domestic Fowl.

The eggshells of the cormorant (Phalacrocorax carbo), domestic fowl (Gallus domesticus), gannet (Sula bassana), guinea fowl (Numida meleagris), greater flamingo (Phoenicopterus ruber), and shag (Phalacrocorax aristotelis) have been separated into two groups on the basis of the composition of their outer stratum. In the domestic fowl, guinea fowl and greater flamingo the outer stratum is an organic cuticle while in the sea-birds it is an inorganic cover rich in vaterite. The calcareous deposits on the membranes of eggs of the domestic fowl which are shell-less at oviposition have been shown to consist essentially of the vaterite form of calcium carbonate. Reasons for the occurrence of this polymorph of calcium carbonate are discussed with relation to the physiology of the birds.