1. Introduction
Spermatogenic cells are connected by cytoplasmic (or intercellular)
bridges as a result of the incomplete cytokinesis.
These bridges make a syncytial cluster of spermatogenic
cells that remain in cytoplasmic continuity throughout their
differentiation in almost all animals including the black snail,
Semisulcospira libertina. This arrangement of spermatogenic
cells is probably responsible for the synchrony of development
of large numbers of germ cells.
The bridge plasma membrane is a specialized membrane
having few intramembranous particles (Weber and Russel,
1987; Yasuzumi et al., 1988) and no cholesterol (Yasuzumi
et al., 1988). These characteristics of the bridge plasma membrane
imply that the membrane has a specific function such
as barrier zone of membrane fluidity.