The cyst shell consists of three layers:
• alveolar layer: a hard layer consisting of lipoproteins impregnated with chitin and haematin;
the haematin concentration determines the colour of the shell, i.e. from pale to dark brown.
Its main function is to provide protection for the embryo against mechanical disruption and
UV radiation. This layer can be completely removed (dissolved) by oxidation treatment with
hypochlorite (= cyst decapsulation, see 4.2.3.).
• outer cuticular membrane: protects the embryo from penetration by molecules larger than
the CO2 molecule (= multilayer membrane with very special filter function; acts as a
permeability barrier).
• embryonic cuticle: a transparent and highly elastic layer separated from the embryo by the
inner cuticular membrane (develops into the hatching membrane during hatching incubation).