ABSTRACT
The fact that fertilized sea-urchin eggs are deformed by fixation with glutaraldehyde (GA) is a well-known cause of concern for electron microscopists. Moreover, fertilized eggs freed from the investments, the fertilization envelope and hyaline layer (HL), are capable of retaining their spherical shape upon GA fixation, indicating that either or both these structures must be responsible for this deformation. To elucidate which structure causes deformation, eggs of the sea urchin, Hemicentrotus pulcherrimus, were freed from the vitelline coat before insemination so that no fertilization envelope is formed. This finding allowed examination by light microscopy of HL formation in a large number of eggs. The chapter reveals that no HL was formed in the eggs cultured in Ca-, Mg-free artificial sea water (ASW) for about 8 min beginning 1–1.5 min after insemination, whereas it was formed in Ca-free ASW.
