T. Blevezacheo et al., ULTRASTRUCTURAL STUDIES ON THE NEMATODE XIPHINEMA-DIVERSICAUDATUM - EGG-SHELL FORMATION, Tissue & cell, 25(3), 1993, pp. 363-374
The ultrastructure of the formation of the egg shell in the longidorid
nematode Xiphinema diversicaudatum is described. Upon fertilization a
vitelline membrane, which constitutes the vitelline layer of the egg
shell, is formed. The chitinous layer is secreted in the perivitelline
space, between the vitelline layer and the egg cell membrane. On comp
letion of the chitinous layer, the material of the lipid layer is extr
uded from the egg cytoplasm to the outer surface, through finger-like
projections. Both chitinous and lipid layers are secreted by granules
in the egg cytoplasm that disappear as the layers are completed. Chiti
nous and lipid layers are formed during the passage of the egg through
the oviduct. The vitelline layer is enriched with secretions produced
by the oviduct cells and then by phospholipids secreted by the cells
of the pars dilatata oviductus. The inner uterine layer is also formed
by deposition of secretory products apposed on the egg shell in the d
istal uterine region and Z-differentiation. In the proximal part of th
e uterus, the egg has a discontinuous electron-dense layer, the extern
al uterine layer. Tangential sections between chitinous and uterine la
yers revealed the presence of holes, possibly egg pores, delimited by
the two uterine layers.