The histochemical and phase contrast observations on the embryonic envelopes enclosing the acanthor of Acanthosentis sp. reveal the presence of 3 layers. All 3 layers are non-refractile during early stages of formation and become refringent subsequently. The outer layer loses its refractile property together with affinity for acid and basic dyes when the eggs are fully developed. This layer is neither tanned nor chitinous. The 2nd layer consists of glyco-lipo protein aceous matrix. The polysaccharide moiety is identified to be strongly sulfated acid mucopolysaccharide. The lipid component is characterized to be KOH resistant and esters of unsaturated fatty acid. The protein is rich in aromatic amino acids. The 3rd and innermost layer contains chitin and acid mucopolysacchardies. The protein is rich in S-containing amino acids. Sulphydryl groups were present during early stages of its formation, but forms disulfhide cross-links subsequently. Stages in the development of acanthors were characterized with reference to the formation of envelopes. The permeability experiments carried out on fresh eggs using 0.1% aqueous solutions of bromophenol blue, methylene blue, toluidine blue, basic fuchsin and neutral red indicate that the inward diffusion of these substances is prevented subsequent to formation of disulfide groups in the innermost layer. The embryo probably derives nutritive requirements from the pseudocoel fluid of the female worm through the envelopes covering it.
