Acrosome
Acrosome in Phallusia nigra


Fig. A Scanning electron microscope (SEM) image of Phallusia nigra spematozoa. M,mitochondrion; Bar: 1um.
Fig. B Sagittal section through the head. There is no midpiece. M,mitochondrion; N,nucleus; Bar: 1um.
Figs. C,D Serial sagittal sections through the apex of the head. Three membrane-bound vesicles or the moderately electron-dense material (MEDM) are present at the apex between the plasmalemma and the nuclear membranes.
The inner and outer nuclear membranes come into close contact with each other to make a "dense line" (arrow). F, fuzzy material; Bar: 200nm ( This is also the magnification for Figs.D-G).
Fig. E Transverse section through the apex of the head at the level of the vesicles. The MEDM occupies the central region of the apex between the plasmalemma and the nuclear membrane dense line. A vesicle is seen on one side of the MEDM. F,fuzzy material; N,nucleus.
Figs. F.G Frontal sections parallel to the apical surface of the head.
Three (Fig.F) or four (Fig.G) vesicles are present in a line alongside the MEDM. F, fuzzy material.

for details: Roux's Arch.Dev.Biol.202:321-328 (1993)